# Python 2.1 Quick Reference

## Contents

- Front matter
- Invocation Options
- Environment Variables
- Lexical Entities : keywords, identifiers, strings, numbers, sequences, dictionaries, operators
- Basic Types And Their Operations
- Advanced Types
- Statements
- Built In Functions
- Built In Exceptions
- Standard methods & operators redefinition in user-created Classes
- Special informative state attributes for some types
- Important Modules : sys, os, posix, posixpath, shutil, time, string, re, math, getopt
- List of modules In base distribution
- Workspace Exploration And Idiom Hints
- Python Mode for Emacs
- The Python Debugger

Version 2.1.3
The Python Quick Reference home page, where you'll find the latest version.
7 Aug 2001 upgraded by Simon Brunning for Python 2.1
16 May 2001 upgraded by Richard Gruet and Simon Brunning for Python 2.0
2000/07/18 upgraded by Richard Gruet, rjgruet@yahoo.com for Python 1.5.2 from V1.3 ref
1995/10/30, by Chris Hoffmann, choffman@vicorp.com

NB: features added in 2.1 since 2.0 are coloured dark green.

NB: features added in 2.0 since 1.5.2 are coloured dark magenta.

Based on:
Python Bestiary, Author: Ken Manheimer, ken.manheimer@nist.gov
Python manuals, Authors: Guido van Rossum and Fred Drake
What's new in Python 2.0, Authors: A.M. Kuchling and Moshe Zadka
python-mode.el, Author: Tim Peters, tim_one@email.msn.com
and the readers of comp.lang.python
Python's nest: http://www.python.org
Development: http://python.sourceforge.net/
ActivePython : http://www.ActiveState.com/ASPN/Python/
newsgroup: comp.lang.python
Help desk: help@python.org
Resources: http://starship.python.net/ and http://www.vex.net/parnassus/
Full documentation: http://www.python.org/doc/
An excellent Python reference book: Python Essential Reference by David Beazley (New Riders)

## Invocation Options

python [-diOStuUvxX?] [-c command | script | - ] [args]

Invocation Options
Option | Effect
--- | ---
-d | Outputs parser debugging information (also PYTHONDEBUG=x)
-i | Inspect interactively after running script (also PYTHONINSPECT=x) and force prompts, even if stdin appears not to be a terminal
-O | Optimize generated bytecode (set __debug__ = 0 =>s suppresses asserts)
-S | Don't perform 'import site' on initialization
-t | Issue warnings about inconsistent tab usage (-tt: issue errors)
-u | Unbuffered binary stdout and stderr (also PYTHONUNBUFFERED=x).
-U | Force Python to interpret all string literals as Unicode literals.

-v | Verbose (trace import statements) (also PYTHONVERBOSE=x)
-x | Skip first line of source, allowing use of non-unix Forms of #!cmd
-X | Disable class based built-in exceptions (for backward compatibility management of exceptions)
-? | Help!
-c command | Specify the command to execute (see next section). This terminates the option list (following options are passed as arguments to the command).
script | the name of a python file (.py) to execute read from stdin. Anything afterward is passed as options to python script or command, not interpreted as an option to interpreter itself.
args | passed to script or command (in sys.argv[1:])
| If no script or command, Python enters interactive mode.

- Available IDEs in std distrib: IDLE (tkinter based, portable), Pythonwin (Windows).

## Environment variables

Environment variables
Variable | Effect
--- | ---
PYTHONHOME | Alternate prefix directory (or prefix;exec_prefix). The default module search path uses prefix/lib
PYTHONPATH | Augments the default search path for module files. The format is the same as the shell's $PATH: one or more directory pathnames separated by ':' or ';' without spaces around (semi-)colons! On Windows first search for Registry key HKEY_LOCAL_MACHINE\Software\Python\PythonCore\x.y\PythonPath (default value). You may also define a key named after your application with a default string value giving the root directory path of your app.
PYTHONSTARTUP | If this is the name of a readable file, the Python commands in that file are executed before the first prompt is displayed in interactive mode (no default).
PYTHONDEBUG | If non-empty, same as -d option
PYTHONINSPECT | If non-empty, same as -i option
PYTHONSUPPRESS | If non-empty, same as -s option
PYTHONUNBUFFERED | If non-empty, same as -u option
PYTHONVERBOSE | If non-empty, same as -v option
PYTHONCASEOK | If non-empty, ignore case in file/module names (imports)

## Notable lexical entities

### Keywords

>     and       del       for       is        raise
>     assert    elif      from      lambda    return
>     break     else      global    not       try
>     class     except    if        or        while
>     continue  exec      import    pass
>     def       finally   in        print

- (list of keywords in std module: keyword)
- Illegitimate Tokens (only valid in strings): @ $ ?
- A statement must all be on a single line. To break a statement over multiple lines use "\", as with the C preprocessor.
- Exception: can always break when inside any (), [], or {} pair, or in triple-quoted strings.
- More than one statement can appear on a line if they are separated with semicolons (";").
- Comments start with "#" and continue to end of line.

### Identifiers

(letter | "_") (letter | digit | "_")*

- Python identifiers keywords, attributes, etc. are case-sensitive.
- Special forms: _ident (not imported by 'from module import *'); __ident__ (system defined name);
- __ident (class-private name mangling)

String literals
Literal
"a string enclosed by double quotes"
'another string delimited by single quotes and with a " inside'
'''a string containing embedded newlines and quote (') marks, can be delimited with triple quotes.'''
""" may also use 3- double quotes as delimiters """
u'a unicode string'
U"Another unicode string"
r'a raw string where \ are kept (literalized): handy for regular expressions and windows paths!'
R"another raw string" -- raw strings cannot end with a \
ur'a unicode raw string'
UR"another raw unicode"

- Use \ at end of line to continue a string on next line.
- adjacent strings are concatened, e.g. 'Monty' ' Python' is the same as 'Monty Python'.
- u'hello' + ' world' --> u'hello world' (coerced to unicode)

String Literal Escapes
Escape | Meaning
--- | ---
\newline | Ignored (escape newline)
\\ | Backslash (\)
\e | Escape (ESC)
\v | Vertical Tab (VT)
\' | Single quote (')
\f | Formfeed (FF)
\OOO | char with octal value OOO
\" | Double quote (")
\n | Linefeed (LF)
\a | Bell (BEL)
\r | Carriage Return (CR)
\xHH | char with hex value HH
\b | Backspace (BS)
\t | Horizontal Tab (TAB)
\uHHHH | unicode char with hex value HHHH, can only be used in unicode string
\UHHHHHHHH | unicode char with hex value HHHHHHHH, can only be used in unicode string
\AnyOtherChar | left as-is

- NUL byte (\000) is NOT an end-of-string marker; NULs may be embedded in strings.
- Strings (and tuples) are immutable: they cannot be modified.

### Numbers

> - Decimal integer: 1234, 1234567890546378940L (or l)
> - Octal integer: 0177, 0177777777777777777L (begin with a 0)
> - Hex integer: 0xFF, 0XFFFFffffFFFFFFFFFFL (begin with 0x or 0X)
> - Long integer (unlimited precision): 1234567890123456L (ends with L or l)
> - Float (double precision): 3.14e-10, .001, 10., 1E3
> - Complex: 1J, 2+3J, 4+5j (ends with J or j, + separates (float) real and imaginary parts)

### Sequences

- String of length 0, 1, 2 (see above)
- '', '1', "12", 'hello\n'
- Tuple of length 0, 1, 2, etc:
- () (1,) (1,2) # parentheses are optional if len > 0
- List of length 0, 1, 2, etc:
- [] [1] [1,2]

Indexing is 0-based. Negative indices (usually) mean count backwards from end of sequence.

Sequence slicing [starting-at-index : but-less-than-index]. Start defaults to '0'; End defaults to 'sequence-length'.

a = (0,1,2,3,4,5,6,7)
a[3] ==> 3
a[-1] ==> 7
a[2:4] ==> (2, 3)
a[1:] ==> (1, 2, 3, 4, 5, 6, 7)
a[:3] ==> (0, 1, 2)
a[:] ==> (0,1,2,3,4,5,6,7) # makes a copy of the sequence.

### Dictionaries (Mappings)

> Dictionary of length 0, 1, 2, etc:
> {} {1 : 'first'} {1 : 'first', 'next': 'second'}

### Operators and their evaluation order

Operators and their evaluation order
Highest | Operator | Comment
--- | --- | ---
| , [...] {...} `...` | Tuple, list & dict. creation; string conv.
| s[i] s[i:j] s.attr f(...) | indexing & slicing; attributes, fct calls
| +x, -x, ~x | Unary operators
| x**y | Power
| x*y x/y x%y | mult, division, modulo
| x+y x-y | addition, substraction
| x<<y x>>y | Bit shifting
| x&y | Bitwise and
| x^y | Bitwise exclusive or
| x|y | Bitwise or
| x<y x<=y x>y x>=y x==y x!=y x<>y x is y x is not y x in s x not in s | Comparison, identity, membership
| not x | boolean negation
| x and y | boolean and
| x or y | boolean or
Lowest | lambda args: expr | anonymous function

- Alternate names are defined in module operator (e.g. __add__ and add for +)
- Most operators are overridable

## Basic Types and Their Operations

### Comparisons (defined between *any* types)

Comparisons
Comparison | Meaning | Notes
--- | --- | ---
< | strictly less than | (1)
<= | less than or equal to |
> | strictly greater than |
>= | greater than or equal to |
== | equal to |
!= or <> | not equal to |
is | object identity | (2)
is not | negated object identity | (2)

Notes :
Comparison behavior can be overridden for a given class by defining special method __cmp__.
(1) X < Y < Z < W has expected meaning, unlike C
(2) Compare object identities (i.e. id(object)), not object values.

### Boolean values and operators

Boolean values and operators
Value or Operator | Returns | Notes
--- | --- | ---
None, numeric zeros, empty sequences and mappings | False |
all other values | True |
not x | True if x is False, else True |
x or y | if x is False then y, else x | (1)
x and y | if x is False then x, else y | (1)

Notes :
Truth testing behavior can be overridden for a given class by defining special method __nonzero__.
(1) Evaluate second arg only if necessary to determine outcome.

### None

> None is used as default return value on functions. Built-in single object with type NoneType.
> Input that evaluates to None does not print when running Python interactively.

### Numeric types

#### Floats, integers and long integers.

> Floats are implemented with C doubles.
> Integers are implemented with C longs.
> Long integers have unlimited size (only limit is system resources)

#### Operators on all numeric types

Operators on all numeric types
Operation | Result
--- | ---
abs(x) | the absolute value of x
int(x) | x converted to integer
long(x) | x converted to long integer
float(x) | x converted to floating point
-x | x negated
+x | x unchanged
x + y | the sum of x and y
x - y | difference of x and y
x * y | product of x and y
x / y | quotient of x and y
x % y | remainder of x / y
divmod(x, y) | the tuple (x/y, x%y)
x ** y | x to the power y (the same as pow(x, y))

#### Bit operators on integers and long integers

Bit operators
Operation | >Result
--- | ---
~x | the bits of x inverted
x ^ y | bitwise exclusive or of x and y
x & y | bitwise and of x and y
x | y | bitwise or of x and y
x << n | x shifted left by n bits
x >> n | x shifted right by n bits

#### Complex Numbers

- represented as a pair of machine-level double precision floating point numbers.
- The real and imaginary value of a complex number z can be retrieved through
- the attributes z.real and z.imag.

#### Numeric exceptions

TypeError
  raised on application of arithmetic operation to non-number
OverflowError
  numeric bounds exceeded
ZeroDivisionError
  raised when zero second argument of div or modulo op

### Operations on all sequence types (lists, tuples, strings)

Operations on all sequence types
Operation | Result | Notes
--- | --- | ---
x in s | 1 if an item of s is equal to x, else 0 |
x not in s | 0 if an item of s is equal to x, else 1 |
s + t | the concatenation of s and t |
s * n, n*s | n copies of s concatenated |
s[i] | i'th item of s, origin 0 | (1)
s[i:j] | slice of s from i (included) to j (excluded) | (1), (2)
len(s) | length of s |
min(s) | smallest item of s |
max(s) | largest item of (s) |

    Notes :

(1) if i or j is negative, the index is relative to the end of the string, ie len(s)+ i or len(s)+j is
substituted. But note that -0 is still 0.
(2) The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j.
If i or j is greater thanlen(s), use len(s). If i is omitted, use len(s). If i is greater than or
equal to j, the slice is empty.

### Operations on mutable (=modifiable) sequences (lists)

Operations on mutable sequences
Operation | Result | Notes
--- | --- | ---
s[i] =x | item i of s is replaced by x |
s[i:j] = t | slice of s from i to j is replaced by t |
del s[i:j] | same as s[i:j] = [] |
s.append(x) | same as s[len(s) : len(s)] = [x] |
s.extend(x) | same as s[len(s):len(s)]= x | (5)
s.count(x) | return number of i's for which s[i] == x |
s.index(x) | return smallest i such that s[i] == x | (1)
s.insert(i, x) | same as s[i:i] = [x] if i >= 0 |
s.remove(x) | same as del s[s.index(x)] | (1)
s.pop([i]) | same as x = s[i]; del s[i]; return x | (4)
s.reverse() | reverse the items of s in place | (3)
s.sort([cmpFct]) | sort the items of s in place | (2), (3)

Notes :
(1) raise a ValueError exception when x is not found in s (i.e. out of range).
(2) The sort() method takes an optional argument specifying a comparison fct of 2 arguments (list items) which should
return -1, 0, or 1 depending on whether the 1st argument is considered smaller than, equal to, or larger than the 2nd
argument. Note that this slows the sorting process down considerably.
(3) The sort() and reverse() methods modify the list in place for economy of space when sorting or reversing a large list.
They don't return the sorted or reversed list to remind you of this side effect.
(4) The pop() method is not supported by mutable sequence types other than lists.
The optional argument i defaults to -1, so that by default the last item is removed and returned.
(5) Raises an exception when x is not a list object.

### Operations on mappings (dictionaries)

Operations on mappings
Operation | Result | Notes
--- | --- | ---
len(d) | the number of items in d |
d[k] | the item of d with key k | (1)
d[k] = x | set d[k] to x |
del d[k] | remove d[k] from d | (1)
d.clear() | remove all items from d |
d.copy() | a shallow copy of d |
d.has_key(k) | 1 if d has key k, else 0 |
d.items() | a copy of d's list of (key, item) pairs | (2)
d.keys() | a copy of d's list of keys | (2)
d1.update(d2) | for k, v in d2.items(): d1[k] = v | (3)
d.values() | a copy of d's list of values | (2)
d.get(k,defaultval) | the item of d with key k | (4)
d.setdefault(k,defaultval) | the item of d with key k | (5)
d.popitem() | an arbitrary item of d, and removes item. |

> Notes :
> TypeError is raised if key is not acceptable
> (1) KeyError is raised if key k is not in the map
> (2) Keys and values are listed in random order
> (3) d2 must be of the same type as d1
> (4) Never raises an exception if k is not in the map, instead it returns defaultVal. defaultVal is optional, when not provided and k is not in the map, None is returned.
> (5) Never raises an exception if k is not in the map, instead it returns defaultVal, and adds k to map with value defaultVal. defaultVal is optional. When not provided and k is not in the map, None is returned and added to map.

### Operations on strings

Note that these string methods largely (but not completely) supersede the functions available in the string module.

Operations on strings
Operation | Result | Notes
--- | --- | ---
s.capitalize() | return a copy of s with only its first character capitalized. |
s.center(width) | return a copy of s centered in a string of length width. | (1)
s.count(sub[,start[,end]]) | return the number of occurrences of substring sub in string s. | (2)
s.encode([encoding[,errors]]) | return an encoded version of s. Default encoding is the current default string encoding. | (3)
s.endswith(suffix[,start[,end]]) | return true if s ends with the specified suffix, otherwise return false. | (2)
s.expandtabs([tabsize]) | return a copy of s where all tab characters are expanded using spaces. | (4)
s.find(sub[,start[,end]]) | return the lowest index in s where substring sub is found. Return -1 if sub is not found. | (2)
s.index(sub[,start[,end]]) | like find(), but raise ValueError when the substring is not found. | (2)
s.isalnum() | return true if all characters in s are alphanumeric, false otherwise. | (5)
s.isalpha() | return true if all characters in s are alphabetic, false otherwise. | (5)
s.isdigit() | return true if all characters in s are digit characters, false otherwise. | (5)
s.islower() | return true if all characters in s are lowercase, false otherwise. | (6)
s.isspace() | return true if all characters in s are whitespace characters, false otherwise. | (5)
s.istitle() | return true if string s is a titlecased string, false otherwise. | (7)
s.isupper() | return true if all characters in s are uppercase, false otherwise. | (6)
s.join(seq) | return a concatenation of the strings in the sequence seq, seperated by 's's. |
s.ljust(width) | return s left justified in a string of length width. | (1), (8)
s.lower() | return a copy of s converted to lowercase. |
s.lstrip() | return a copy of s with leading whitespace removed. |
s.replace(old, new[, maxsplit]) | return a copy of s with all occurrences of substring old replaced by new. | (9)
s.rfind(sub[,start[,end]]) | return the highest index in s where substring sub is found. Return -1 if sub is not found. | (2)
s.rindex(sub[,start[,end]]) | like rfind(), but raise ValueError when the substring is not found. | (2)
s.rjust(width) | return s right justified in a string of length width. | (1), (8)
s.rstrip() | return a copy of s with trailing whitespace removed. |
s.split([sep[,maxsplit]]) | return a list of the words in s, using sep as the delimiter string. | (10)
s.splitlines([keepends]) | return a list of the lines in s, breaking at line boundaries. | (11)
s.startswith(prefix[,start[,end]]) | return true if s starts with the specified prefix, otherwise return false. | (2)
s.strip() | return a copy of s with leading and trailing whitespace removed. |
s.swapcase() | return a copy of s with uppercase characters converted to lowercase and vice versa. |
s.title() | return a titlecased copy of s, i.e. words start with uppercase characters, all remaining cased characters are lowercase. |
s.translate(table[,deletechars]) | return a copy of s mapped through translation table table. | (12)
s.upper() | return a copy of s converted to uppercase. |

Notes :
(1) Padding is done using spaces.
(2) If optional argument start is supplied, substring s[start:] is processed. If optional arguments start and end are supplied, substring s[start:end] is processed.
(3) Optional argument errors may be given to set a different error handling scheme. The default for errors is 'strict', meaning that encoding errors raise a ValueError. Other possible values are 'ignore' and 'replace'.
(4) If optional argument tabsize is not given, a tab size of 8 characters is assumed.
(5) Returns false if string s does not contain at least one character.
(6) Returns false if string s does not contain at least one cased character.
(7) A titlecased string is a string in which uppercase characters may only follow uncased characters and lowercase characters only cased ones.
(8) s is returned if width is less than len(s).
(9) If the optional argument maxsplit is given, only the first maxsplit occurrences are replaced.
(10) If sep is not specified or None, any whitespace string is a separator. If maxsplit is given, at most maxsplit splits are done.
(11) Line breaks are not included in the resulting list unless keepends is given and true.
(12) table must be a string of length 256. All characters occurring in the optional argument deletechars are removed prior to translation.

### String formatting with the % operator

formatString % args--> evaluates to a string

- formatString uses C printf format codes : %, c, s, i, d, u, o, x, X, e, E, f, g, G, r (details below).
- Width and precision may be a * to specify that an integer argument gives the actual width or precision.
- The flag characters -, +, blank, # and 0 are understood. (details below)
- %s will convert any type argument to string (uses str() function)
- args may be a single arg or a tuple of args

            '%s has %03d quote types.' % ('Python', 2)  # => 'Python has 002 quote types.'

- Right-hand-side can also be a mapping:

            a = '%(lang)s has %(c)03d quote types.' % {'c':2, 'lang':'Python}

(vars() function very handy to use on right-hand-side.)

Format codes
Conversion | Meaning
--- | ---
d | Signed integer decimal.
i | Signed integer decimal.
o | Unsigned octal.
u | Unsigned decimal.
x | Unsigned hexidecimal (lowercase).
X | Unsigned hexidecimal (uppercase).
e | Floating point exponential format (lowercase).
E | Floating point exponential format (uppercase).
f | Floating point decimal format.
F | Floating point decimal format.
g | Same as "e" if exponent is greater than -4 or less than precision, "f" otherwise.
G | Same as "E" if exponent is greater than -4 or less than precision, "F" otherwise.
c | Single character (accepts integer or single character string).
r | String (converts any python object using repr()).
s | String (converts any python object using str()).
% | No argument is converted, results in a "%" character in the result. (The complete specification is %%.)

Conversion flag characters
Flag | Meaning
--- | ---
# | The value conversion will use the ``alternate form''.
0 | The conversion will be zero padded.
- | The converted value is left adjusted (overrides "-").
| (a space) A blank should be left before a positive number (or empty string) produced by a signed conversion.
+ | A sign character ("+" or "-") will precede the conversion (overrides a "space" flag).

### File Objects

Created with built-in function open; may be created by other modules' functions as well.

#### Operators on file objects

File operations
Operation | Result
--- | ---
f.close() | Close file f.
f.fileno() | Get fileno (fd) for file f.
f.flush() | Flush file f's internal buffer.
f.isatty() | 1 if file f is connected to a tty-like dev, else 0.
f.read([size]) | Read at most size bytes from file f and return as a string object. If size omitted, read to EOF.
f.readline() | Read one entire line from file f.
f.readlines() | Read until EOF with readline() and return list of lines read.
f.xreadlines() | Return a sequence-like object for reading a file line-by-line without reading the entire file into memory.
f.seek(offset[, whence=0]) | Set file f's position, like "stdio's fseek()". whence == 0 then use absolute indexing. whence == 1 then offset relative to current pos. whence == 2 then offset relative to file end.
f.tell() | Return file f's current position (byte offset).
f.write(str) | Write string to file f.
f.writelines(list) | Write list of strings to file f.

#### File Exceptions

EOFError
  End-of-file hit when reading (may be raised many times, e.g. if f is a tty).
IOError
  Other I/O-related I/O operation failure

## Advanced Types

-See manuals for more details -

- Module objects
- Class objects
- Class instance objects
- Type objects (see module: types)
- File objects (see above)
- Slice objects
- XRange objects
- Callable types:
- - User-defined (written in Python):
  - - User-defined Function objects
    - User-defined Method objects
  - Built-in (written in C):
  - - Built-in Function objects
    - Built-in Method objects
- Internal Types:
- - Code objects (byte-compile executable Python code: bytecode)
  - Frame objects (execution frames)
  - Traceback objects (stack trace of an exception)

## Statements

Statement | Result
--- | ---
pass | Null statement
del name[,name]* | Unbind name(s) from object. Object will be indirectly(and automatically) deleted only if no longer referenced.
print[>> fileobject,] [s1 [, s2 ]* [,] | Writes to sys.stdout, or to fileobject if supplied. Puts spaces between arguments. Puts newline at endunless statement ends with comma. Print is not required when running interactively, simply typing an expression will print its value, unless the value is None.
exec x [in globals [,locals]] | Executes x in namespaces provided. Defaultsto current namespaces. x can be a string, fileobject or a function object.
callable(value,... [id=value], [*args], [**kw]) | Call function callable with parameters. Parameters can be passed by name or be omitted if functiondefines default values. E.g. if callable is defined as "def callable(p1=1, p2=2)" "callable()" <=> "callable(1, 2)" "callable(10)" <=> "callable(10, 2)" "callable(p2=99)" <=> "callable(1, 99)" *args is a tuple of positional arguments. **kw is a dictionary of keyword arguments.

### Assignment operators

Assignment operators
Operator | Result | Notes
--- | --- | ---
a = b | Basic assignment - assign object b to label a | (1)
a += b | Roughly equivalent to a = a + b | (2)
a -= b | Roughly equivalent to a = a - b | (2)
a *= b | Roughly equivalent to a = a * b | (2)
a /= b | Roughly equivalent to a = a / b | (2)
a %= b | Roughly equivalent to a = a % b | (2)
a **= b | Roughly equivalent to a = a ** b | (2)
a &= b | Roughly equivalent to a = a & b | (2)
a |= b | Roughly equivalent to a = a | b | (2)
a ^= b | Roughly equivalent to a = a ^ b | (2)
a >>= b | Roughly equivalent to a = a >> b | (2)
a <<= b | Roughly equivalent to a = a << b | (2)

Notes :
(1) Can unpack tuples, lists, and strings.
first, second = a[0:2]; [f, s] = range(2); c1,c2,c3='abc'
Tip: x,y = y,x swaps x and y.
(2) Not exactly equivalent - a is evaluated only once. Also, where possible, operation performed in-place - a is modified rather than replaced.

Control flow statements
Statement | Result
--- | ---
if condition: suite [elif condition: suite]* [else: suite] | usual if/else_if/else statement
while condition: suite [else: suite] | usual while statement. "else" suite is executedafter loop exits, unless the loop is exited with"break"
for element in sequence: suite [else: suite] | iterates over sequence, assigning each element to element.Use built-in range function to iterate a number of times."else" suite executed at end unless loop exitedwith "break"
break | immediately exits "for" or "while" loop
continue | immediately does next iteration of "for" or "while" loop
return [result] | Exits from function (or method) and returns result (use a tuple to return more than one value). If no result given, then returns None.

Exception statements
Statement | Result
--- | ---
assert expr[, message] | expr is evaluated. if false, raises exception AssertionErrorwith message. Inhibited if __debug__ is 0.
try: suite1 [except [exception [, value]: suite2]+ [else: suite3] | Statements in suite1 are executed. If an exception occurs, lookin "except" clauses for matching <exception>. If matches or bare"except" execute suite of that clause. If no exception happenssuite in "else" clause is executed after suite1.If exception has a value, it is put in value.exception can also be tuple of exceptions, e.g."except (KeyError, NameError), val: print val"
try: suite1 finally: suite2 | Statements in suite1 are executed. If noexception, execute suite2 (even if suite1 isexited with a "return", "break" or "continue"statement). If exception did occur, executessuite2 and then immediately reraises exception.
raise exception [,value [, traceback]] | Raises exception with optional valuevalue. Arg traceback specifies a traceback object touse when printing the exception's backtrace.
raise | A raise statement without arguments re-raises the last exception raised in the current function

- An exception is either a string (object) or (preferably) a class instance.
- Can create a new one simply by creating a new string:

my_exception = 'You did something wrong'
try:
if bad:
raise my_exception, bad
except my_exception, value:
print 'Oops', value

- Exception classes must be derived from the predefined class: Exception, e.g.:

                class text_exception(Exception): pass
                try:
                    if bad:
                        raise text_exception()
                        # This is a shorthand for the form
                        # "raise <class>, <instance>"
                 except Exception:
                     print 'Oops'
                     # This will be printed because
                     # text_exception is a subclass of Exception
    When an error message is printed for an unhandled exception which is a
    class, the class name is printed, then a colon and a space, and
    finally the instance converted to a string using the built-in function
    str().

    All built-in exception classes derives from StandardError, itself
    derived from Exception.

### Name Space Statements

[1.51: On Mac & Windows, the case of module file names must now match the case as used
in the import statement]

    Packages (>1.5): a package is a name space which maps to a directory including
                    module(s) and the special initialization module '__init__.py'
                    (possibly empty). Packages/dirs can be nested. You address a
                    module's symbol via '[package.[package...]module.symbol's.

Name space statements
Statement | Result
--- | ---
import module1 [as name1] [, module2]* | Imports modules. Members of module must bereferred to by qualifying with [package.]module name:"import sys; print sys.argv:""import package1.subpackage.module; package1.subpackage.module.foo()" module1 renamed as name1, if supplied.
from module import name1 [as othername1] [, name2]* | Imports names from module module in current namespace. "from sys import argv; print argv" "from package1 import module; module.foo()" "from package1.module import foo; foo()" name1 renamed as othername1, if supplied.
from module import * | Imports all names in module, except those starting with "_" *to be used sparsely, beware of name clashes* "from sys import *; print argv" "from package.module import *; print x' Only legal at the top level of a module. If module defines an __all__ attribute, only names listed in __all__ will be imported. NB: "from package import *" only imports the symbols definedin the package's __init__.py file, not those in the template modules!
global name1 [, name2] | Names are from global scope (usually meaning from module) rather than local (usually meaning only in function). E.g. in function without "global" statements, assuming "a" is name that hasn't been used in function or module so far: - Try to read from "a" -> NameError - Try to write to "a" -> creates "a" local to function If "a" not defined in fct, but is in module, then: - Try to read from "a", gets value from module - Try to write to "a", creates "a" local to fct But note "a[0]=3" starts with search for "a", will use to global "a" if no local "a".

### Function Definition

    def func_id ([param_list]): suite
                    -- Creates a function object & binds it to name func_id.

>     param_list ::= [id [, id]*]
>     id ::= value | id = value | *id | **id

>     [Args are passed by value.Thus only args representing a mutable object
>     can be modified (are inout parameters). Use a tuple to return more than
>     one value]

    Example:
        def test (p1, p2 = 1+1, *rest, **keywords):
                -- Parameters with "=" have default value (v is
                   evaluated when function defined).
                   If list has "*id" then id is assigned a tuple of
                   all remaining args passed to function (like C vararg)
                   If list has "**id" then id is assigned a dictionary of
                   all extra arguments passed as keywords.

### Class Definition

    class <class_id> [(<super_class1> [,<super_class2>]*)]: <suite>
            -- Creates a class object and assigns it name <class_id>
               <suite> may contain local "defs" of class methods and
               assignments to class attributes.
    Example:
        class my_class (class1, class_list[3]): ...
                      Creates a class object inheriting from both "class1" and whatever
                      class object "class_list[3]" evaluates to. Assigns new
                      class object to name "my_class".
            - First arg to class methods is always instance object, called 'self'
              by convention.
            - Special method __init__() is called when instance is created.
            - Special method __del__() called when no more reference to object.
            - Create instance by "calling" class object, possibly with arg
              (thus instance=apply(aClassObject, args...) creates an instance!)
            - In current implementation, can't subclass off built-in
              classes. But can "wrap" them, see UserDict & UserList modules,
              and see __getattr__() below.
    Example:
         class c (c_parent):
               def __init__(self, name): self.name = name
               def print_name(self): print "I'm", self.name
               def call_parent(self): c_parent.print_name(self)
               instance = c('tom')
               print instance.name
               'tom'
               instance.print_name()
               "I'm tom"
            Call parent's super class by accessing parent's method
            directly and passing "self" explicitly (see "call_parent"
            in example above).
            Many other special methods available for implementing
            arithmetic operators, sequence, mapping indexing, etc.

#### Documentation Strings

Modules, classes and functions may be documented by placing a string literal by itself as the first statement in the suite. The documentation can be retrieved by getting the '__doc__' attribute from the module, class or function.

    Example:
         class C:
                "A description of C"
                def __init__(self):
                    "A description of the constructor"
                    # etc.
    Then c.__doc__ == "A description of C".
    Then c.__init__.__doc__ == "A description of the constructor".

### Others

    lambda [param_list]: returnedExpr
                    -- Creates an anonymous function. returnedExpr must be
                       an expression, not a statement (e.g., not "if xx:...",
                       "print xxx", etc.) and thus can't contain newlines.
                       Used mostly for filter(), map(), reduce() functions, and GUI callbacks..

List comprehensions

    result = [expression for item1 in sequence1  [if condition1]
                            [for item2 in sequence2 ... for itemN in sequenceN]
                          ]

is equivalent to:

    result = []
    for item1 in sequence1:
        for item2 in sequence2:
        ...
            for itemN in sequenceN:
                 if (condition1) and further conditions:
                      result.append(expression)

## Built-In Functions

Built-In Functions
Function | Result
--- | ---
__import__(name[, globals[, locals[, from list]]]) | Imports module within the given context (see lib ref for more details)
abs(x) | Return the absolute value of number x.
apply(f, args[, keywords]) | Calls func/method f with arguments args and optional keywords.
callable(x) | Returns 1 if x callable, else 0.
chr(i) | Returns one-character string whose ASCII code isinteger i
cmp(x,y) | Returns negative, 0, positive if x <, ==, > to y
coerce(x,y) | Returns a tuple of the two numeric arguments converted to a common type.
compile(string, filename, kind) | Compiles string into a code object. filename is used in error message, can be any string. It is usually the file from which the code was read, or eg. '<string>'if not read from file.kind can be 'eval' if string is a single stmt, or 'single' which prints the output of expression statements that evaluate to something else than None, or be 'exec'.
complex(real[, image]) | Builds a complex object (can also be done using J or j suffix,e.g. 1+3J)
delattr(obj, name) | deletes attribute named name of object obj <=> del obj.name
dir([object]) | If no args, returns the list of names in current local symbol table. With a module, class or class instance object as arg, returns list of names in its attr. dict.
divmod(a,b) | Returns tuple of (a/b, a%b)
eval(s[, globals[, locals]]) | Eval string s in (optional) globals, locals contexts. s must have no NUL's or newlines. s can also be a code object.Example: x = 1; incr_x = eval('x + 1')
execfile(file[, globals[, locals]]) | Executes a file without creating a new module, unlike import.
filter(function, sequence) | Constructs a list from those elements of sequence for whichfunction returns true. function takes one parameter.
float(x) | Converts a number or a string to floating point.
getattr(object, name[, default])) | Gets attribute called name from object,e.g. getattr(x, 'f') <=> x.f). If not found, raises AttributeError or returns default if specified.
globals() | Returns a dictionary containing current global variables.
hasattr(object, name) | Returns true if object has attr called name.
hash(object) | Returns the hash value of the object (if it has one)
hex(x) | Converts a number x to a hexadecimal string.
id(object) | Returns a unique 'identity' integer for an object.
input([prompt]) | Prints prompt if given. Reads input and evaluates it.
int(x[, base]) | Converts a number or a string to a plain integer. Optional base paramenter specifies base from which to convert string values.
intern(aString) | Enters aString in the table of "interned strings" and returns the string. Interned strings are 'immortals'.
isinstance(obj, class) | returns true if obj is an instance of class. If issubclass(A,B) then isinstance(x,A) => isinstance(x,B)
issubclass(class1, class2) | returns true if class1 is derived from class2
len(obj) | Returns the length (the number of items) of an object (sequence, dictionary, or instance of class implementing __len__).
list(sequence) | Converts sequence into a list. If already a list, returns a copy of it.
locals() | Returns a dictionary containing current local variables.
long(x[, base]) | Converts a number or a string to a long integer. Optional base paramenter specifies base from which to convert string values.
map(function, list, ...) | Applies function to every item of list and returns a list of the results. If additional arguments are passed, function must take that many arguments and it is givent o function on each call.
max(seq) | Returns the largest item of the non-empty sequence seq.
min(seq) | Returns the smallest item of a non-empty sequence seq.
oct(x) | Converts a number to an octal string.
open(filename [, mode='r', [bufsize=implementation dependent]]) | Returns a new file object. filename is the file name to be opened. mode indicates how the file is to be opened: 'r' for reading 'w' for writing (truncating an existing file) 'a' opens it for appending '+' (appended to any of the previous modes) open the file for updating (note that 'w+' truncates the file) 'b' (appended to any of the previous modes) open the file in binary mode bufsize is 0 for unbuffered, 1 for line-buffered, negative for sys-default, all else, of (about) given size.
ord(c) | Returns integer ASCII value of c (a string of len 1). Works with Unicode char.
pow(x, y [, z]) | Returns x to power y [modulo z]. See also ** operator.
range(start [,end [, step]]) | Returns list of ints from >= start and < end. With 1 arg, list from 0..arg-1 With 2 args, list from start..end-1 With 3 args, list from start up to end by step
raw_input([prompt]) | Prints prompt if given, then reads string from std input (no trailing \n). See also input().
reduce(f, list [, init]) | Applies the binary function f to the items oflist so as to reduce the list to a single value.I f init given, it is "prepended" to list.
reload(module) | Re-parses and re-initializes an already imported module. Useful in interactive mode, if you want to reload a module after fixing it. If module was syntactically correct but had an error in initialization, must import it one more time before calling reload().
repr(object) | Returns a string containing a printable and if possible evaluable representation of an object. <=> `object` (using backquotes). Class redefineable (__repr__). See also str()
round(x, n=0) | Returns the floating point value x rounded to n digits after the decimal point.
setattr(object, name, value) | This is the counterpart of getattr().setattr(o, 'foobar', 3) <=> o.foobar = 3 Creates attribute if it doesn't exist!
slice([start,] stop[, step]) | Returns a slice object representing a range, with R/O attributes: start, stop, step.
str(object) | Returns a string containing a nicely printable representation of an object. Class overridable (__str__).See also repr().
tuple(sequence) | Creates a tuple with same elements as sequence. If already a tuple, return itself (not a copy).
type(obj) | Returns a type object [see module types] representing the type of obj. Example: import types if type(x) == types.StringType: print 'It is a string'NB: it is recommended to use the following form:if isinstance(x, types.StringType): etc...
unichr(code) | Returns a unicode string 1 char long with given code.
unicode(string[, encoding[, error]]]) | Creates a Unicode string from a 8-bit string, using the given encoding name and error treatment ('strict', 'ignore',or 'replace'}.
vars([object]) | Without arguments, returns a dictionary corresponding to the current local symbol table. With a module,class or class instance object as argument returns a dictionary corresponding to the object'ss ymbol table. Useful with "%" formatting operator.
xrange(start [, end [, step]]) | Like range(), but doesn't actually store entire list all at once. Good to use in "for" loops when there is abig range and little memory.
zip(seq1[, seq2, ...]) | Returns a list of tuples where each tuple contains the nth element of each of the argument sequences.

## Built-In Exceptions

Exception
Root class for all exceptions
SystemExit
On 'sys.exit()'
StandardError
Base class for all built-in exceptions; derived from Exception root class.
ArithmeticError
Base class for OverflowError, ZeroDivisionError, FloatingPointError
FloatingPointError
When a floating point operation fails.
OverflowError
  On excessively large arithmetic operation
ZeroDivisionError
  On division or modulo operation with 0 as 2nd arg
  AssertionError
When an assert statement fails.
AttributeError
  On attribute reference or assignment failure
EnvironmentError [new in 1.5.2]
On error outside Python; error arg tuple is (errno, errMsg...)
IOError [changed in 1.5.2]
  I/O-related operation failure
OSError [new in 1.5.2]
  used by the os module's os.error exception.
EOFError
  Immediate end-of-file hit by input() or raw_input()
ImportError
  On failure of `import' to find module or name
KeyboardInterrupt
  On user entry of the interrupt key (often `Control-C')
LookupError
base class for IndexError, KeyError
IndexError
  On out-of-range sequence subscript
KeyError
  On reference to a non-existent mapping (dict) key
MemoryError
  On recoverable memory exhaustion
NameError
  On failure to find a local or global (unqualified) name
RuntimeError
  Obsolete catch-all; define a suitable error instead
  NotImplementedError [new in 1.5.2]
  On method not implemented
SyntaxError
  On parser encountering a syntax error
  IndentationError
  On parser encountering an indentation syntax error
  TabError
  On parser encountering an indentation syntax error
SystemError
  On non-fatal interpreter error - bug - report it
TypeError
  On passing inappropriate type to built-in op or func
ValueError
  On arg error not covered by TypeError or more precise

## Standard methods & operators redefinition in classes

    Standard methods & operators map to special '__methods__' and thus may be
     redefined (mostly in in user-defined classes), e.g.:
        class x:
             def __init__(self, v): self.value = v
             def __add__(self, r): return self.value + r
        a = x(3) # sort of like calling x.__init__(a, 3)
        a + 4    # is equivalent to a.__add__(4)

Special methods for any class
Method | Description
--- | ---
__init__(self, args) | Instance initialization (on construction)
__del__(self) | Called on object demise (refcount becomes 0)
__repr__(self) | repr() and `...` conversions
__str__(self) | str() and 'print' statement
__cmp__(self, other) | Compares self to other and returns <0, 0, or >0. Implements >, <, == etc...
__lt__(self, other) | Called for self < other comparisons. Can return anything, or can raise an exception.
__le__(self, other) | Called for self <= other comparisons. Can return anything, or can raise an exception.
__gt__(self, other) | Called for self > other comparisons. Can return anything, or can raise an exception.
__ge__(self, other) | Called for self >= other comparisons. Can return anything, or can raise an exception.
__eq__(self, other) | Called for self == other comparisons. Can return anything, or can raise an exception.
__ne__(self, other) | Called for self != other (and self <> other) comparisons. Can return anything, or can raise an exception.
__hash__(self) | Compute a 32 bit hash code; hash() and dictionary ops
__nonzero__(self) | Returns 0 or 1 for truth value testing
__getattr__(self, name) | Called when attr lookup doesn't find <name>
__setattr__(self, name, value) | Called when setting an attr (inside, don't use "self.name = value", use "self.__dict__[name] = value")
__delattr__(self, name) | Called to delete attr <name
__call__(self, *args) | called when an instance is called as function.

### Operators

> See list in the operator module. Operator function names are provided with 2 variants, with or without leading & trailing '__' (eg. __add__ or add).

Numeric operations special methods
Operation | Special method
--- | ---
self+other | __add__(self,other)
self-other | __sub__(self,other)
self*other | __mul__(self,other)
self/other | __div__(self,other)
self%other | __mod__(self,other)
divmod(self,other) | __divmod__(self,other)
self**other | __pow__(self,other)
self&other | __and__(self,other)
self^other | __xor__(self,other)
self|other | __or__(self,other)
self<<other | __lshift__(self,other)
self>>other | __rshift__(self,other)
nonzero(self) | __nonzero__(self) (used in boolean testing)
-self | __neg__(self)
+self | __pos__(self)
abs(self) | __abs__(self)
~self | __invert__(self) (bitwise)
self+=other | __iadd__(self,other)
self-=other | __isub__(self,other)
self*=other | __imul__(self,other)
self/=other | __idiv__(self,other)
self%=other | __imod__(self,other)
self**=other | __ipow__(self,other)
self&=other | __iand__(self,other)
self^=other | __ixor__(self,other)
self|=other | __ior__(self,other)
self<<=other | __ilshift__(self,other)
self>>=other | __irshift__(self,other)

Conversions
Method | Descripion
--- | ---
int(self) | __int__(self)
long(self) | __long__(self)
float(self) | __float__(self)
complex(self) | __complex__(self)
oct(self) | __oct__(self)
hex(self) | __hex__(self)
coerce(self,other) | __coerce__(self,other)

Right-hand-side equivalents for all binary operators exist; are called when class instance is on r-h-s of operator:
a + 3 calls __add__(a, 3)
3 + a calls __radd__(a, 3)

Special operations for some types
| Operation | Special method | Notes
--- | --- | --- | ---
All sequences and maps:
| len(s) | __len__(s) | length of object, >= 0. Length 0 == false
| s[i] | __getitem__(s,i) | Element at index/key i, origin 0
Sequences, general methods, plus:
| s[i]=v | __setitem__(s,i,v) |
| del s[i] | __delitem__(s,i) |
| s[i:j] | __getslice__(s,i,j) |
| s[i:j]=seq | __setslice__(s,i,j,seq) |
| del s[i:j] | __delslice__(s,i,j) | s[i:j] = []
| seq * n | __repeat__(seq, n) |
| s1 + s2 | = __concat__(s1, s2) |
| i in s | __contains__(s, i) |
Mappings, general methods, plus
| hash(s) | = __hash__(s) | hash value for dictionary references
| s[k]=v | = __setitem__(s,k,v) |
| del s[k] | = __delitem__(s,k) |

## Special informative state attributes for some types:

Lists & Dictionaries
Attribute | Meaning
--- | ---
__methods__ | (list, R/O): list of method names of the object

Modules
Attribute | Meaning
--- | ---
__doc__ | (string/None, R/O): doc string (<=> __dict__['__doc__'])
__name__ | (string, R/O): module name (also in __dict__['__name__'])
__dict__ | (dict, R/O): module's name space
__file__ | (string/undefined, R/O): pathname of .pyc, .pyo or .pyd (undef for modules statically linked to the interpreter)
__path__ | (string/undefined, R/O): fully qualified package name when applies.

Classes
Attribute | Meaning
--- | ---
__doc__ | (string/None, R/W): doc string (<=> __dict__['__doc__'])
__name__ | (string, R/W): class name (also in __dict__['__name__'])
__bases__ | (tuple, R/W): parent classes
__dict__ | (dict, R/W): attributes (class name space)

Instances
Attribute | Meaning
--- | ---
__class__ | (class, R/W): instance's class
__dict__ | (dict, R/W): attributes

User defined functions
Attribute | Meaning
--- | ---
__doc__ | (string/None, R/W): doc string
__name__ | (string, R/O): function name
func_doc | (R/W): same as __doc__
func_name | (R/O): same as __name__
func_defaults | (tuple/None, R/W): default args values if any
func_code | (code, R/W): code object representing the compiled function body
func_globals | (dict, R/O): ref to dictionary of func global variables

User-defined Methods
Attribute | Meaning
--- | ---
__doc__ | (string/None, R/O): doc string
__name__ | (string, R/O): method name (same as im_func.__name__)
im_class | (class, R/O): class defining the method (may be a base class)
im_self | (instance/None, R/O): target instance object (None if unbound)
im_func | (function, R/O): function object

Built-in Functions & methods
Attribute | Meaning
--- | ---
__doc__ | (string/None, R/O): doc string
__name__ | (string, R/O): function name
__self__ | [methods only] target object
__members__ | list of attr names: ['__doc__','__name__','__self__'])

Codes
Attribute | Meaning
--- | ---
co_name | (string, R/O): function name
co_argcount | (int, R/0): number of positional args
co_nlocals | (int, R/O): number of local vars (including args)
co_varnames | (tuple, R/O): names of local vars (starting with args)
co_code | (string, R/O): sequence of bytecode instructions
co_consts | (tuple, R/O): literals used by the bytecode, 1st one is function doc (or None)
co_names | (tuple, R/O): names used by the bytecode
co_filename | (string, R/O): filename from which the code was compiled
co_firstlineno | (int, R/O): first line number of the function
co_lnotab | (string, R/O): string encoding bytecode offsets to line numbers.
co_stacksize | (int, R/O): required stack size (including local vars)
co_firstlineno | (int, R/O): first line number of the function
co_flags | (int, R/O): flags for the interpreter bit 2 set if fct uses "*arg" syntaxbit 3 set if fct uses '**keywords' syntax

Frames
Attribute | Meaning
--- | ---
f_back | (frame/None, R/O): previous stack frame (toward the caller)
f_code | (code, R/O): code object being executed in this frame
f_locals | (dict, R/O): local vars
f_globals | (dict, R/O): global vars
f_builtins | (dict, R/O): built-in (intrinsic) names
f_restricted | (int, R/O): flag indicating whether fct is executed in restricted mode
f_lineno | (int, R/O): current line number
f_lasti | (int, R/O): precise instruction (index into bytecode)
f_trace | (function/None, R/W): debug hook called at start of each source line
f_exc_type | (Type/None, R/W): Most recent exception type
f_exc_value | (any, R/W): Most recent exception value
f_exc_traceback | (traceback/None, R/W): Most recent exception traceback

Tracebacks
Attribute | Meaning
--- | ---
tb_next | (frame/None, R/O): next level in stack trace (toward the frame where the exception occurred)
tb_frame | (frame, R/O): execution frame of the current level
tb_lineno | (int, R/O): line number where the exception occured
tb_lasti | (int, R/O): precise instruction (index into bytecode)

Slices
Attribute | Meaning
--- | ---
start | (any/None, R/O): lowerbound
stop | (any/None, R/O): upperbound
step | (any/None, R/O): step value

Complex numbers
Attribute | Meaning
--- | ---
real | (float, R/O): real part
imag | (float, R/O): imaginary part

xranges
Attribute | Meaning
--- | ---
tolist | (Built-in method, R/O): ?

## Important Modules

sys

Some sys variables
Variable | Content
--- | ---
argv | The list of command line arguments passed to a Python script. sys.argv[0] is the script name.
builtin_module_names | A list of strings giving the names of all modules written in C that are linked into this interpreter.
check_interval | How often to check for thread switches or signals (measured in number of virtual machine instructions)
exitfunc | User can set to a parameterless function. It will get called before interpreter exits.
last_type, last_value, last_traceback | Set only when an exception not handled and interpreter prints an error. Used by debuggers.
maxint | maximum positive value for integers
modules | Dictionary of modules that have already been loaded.
path | Search path for external modules. Can be modified by program. sys.path[0] == dir of script executing
platform | The current platform, e.g. "sunos5", "win32"
ps1, ps2 | prompts to use in interactive mode.
stdin, stdout, stderr | File objects used for I/O. One can redirect by assigning a new file object to them (or any object: with a method write(string) for stdout/stderr, or with a method readline() for stdin)
version | string containing version info about Python interpreter. (and also: copyright, dllhandle, exec_prefix, prefix)
version_info | tuple containing Python version info - (major, minor, micro, level, serial).

Some sys functions
Function | Result
--- | ---
displayhook | The function used to display the output of commands issued in interactive mode - defaults to the builtin repr().
excepthook | Can be set to a user defined function, to which any uncaught exceptions are passed.
exit(n) | Exits with status n. Raises SystemExit exception.(Hence can be caught and ignored by program)
getrefcount(object) | Returns the reference count of the object. Generally 1 higher than you might expect, because of object arg temp reference.
setcheckinterval(interval) | Sets the interpreter's thread switching interval (in number of virtualcode instructions, default:10).
settrace(func) | Sets a trace function: called before each line ofcode is exited.
setprofile(func) | Sets a profile function for performance profiling.
exc_info() | Info on exception currently being handled; this is atuple (exc_type, exc_value, exc_traceback).Warning: assigning the traceback return value to a local variable in a function handling an exception will cause a circular reference.
setdefaultencoding(encoding) | Change default Unicode encoding - defaults to 7-bit ASCII.
getrecursionlimit() | Retrieve maximum recursion depth.
setrecursionlimit() | Set maximum recursion depth. (Defaults to 1000.)

os
"synonym" for whatever O/S-specific module is proper for current environment. this module uses posix whenever possible.
(see also M.A. Lemburg's utility platform.py)

Some os variables
Variable | Meaning
--- | ---
name | name of O/S-specific module (e.g. "posix", "mac", "nt")
path | O/S-specific module for path manipulations. On Unix, os.path.split() <=> posixpath.split()
curdir | string used to represent current directory ('.')
pardir | string used to represent parent directory ('..')
sep | string used to separate directories ('/' or '\'). Tip: use os.path.join() to build portable paths.
altsep | Alternate sep if applicable (None otherwise)
pathsep | character used to separate search path components (as in $PATH), eg. ';' for windows.
linesep | line separator as used in binary files, ie '\n' on Unix, '\r\n' on Dos/Win, '\r'

Some os functions
Function | Result
--- | ---
makedirs(path[, mode=0777]) | Recursive directory creation (create required intermediary dirs); os.error if fails.
removedirs(path) | Recursive directory delete (delete intermediary empty dirs); if fails.
renames(old, new) | Recursive directory or file renaming; os.error if fails.

posix
don't import this module directly, import os instead !
(see also module: shutil for file copy & remove fcts)

posix Variables
Variable | Meaning
--- | ---
environ | dictionary of environment variables, e.g.posix.environ['HOME'].
error | exception raised on POSIX-related error. Corresponding value is tuple of errno code and perror() string.

Some posix functions
Function | Result
--- | ---
chdir(path) | Changes current directory to path.
chmod(path, mode) | Changes the mode of path to the numeric mode
close(fd) | Closes file descriptor fd opened with posix.open.
_exit(n) | Immediate exit, with no cleanups, no SystemExit,etc. Should use this to exit a child process.
execv(p, args) | "Become" executable p with args args
getcwd() | Returns a string representing the current working directory
getpid() | Returns the current process id
fork() | Like C's fork(). Returns 0 to child, child pid to parent.[Not on Windows]
kill(pid, signal) | Like C's kill [Not on Windows]
listdir(path) | Lists (base)names of entries in directory path, excluding '.' and '..'
lseek(fd, pos, how) | Sets current position in file fd to position pos, expressed as an offset relative to beginning of file (how=0), to current position (how=1), or to end of file (how=2)
mkdir(path[, mode]) | Creates a directory named path with numeric mode (default 0777)
open(file, flags, mode) | Like C's open(). Returns file descriptor. Use file object functions rather than this low level ones.
pipe() | Creates a pipe. Returns pair of file descriptors (r, w) [Not on Windows].
popen(command, mode='r', bufSize=0) | Opens a pipe to or from command. Result is a file object to read to or write from, as indicated by mode being 'r' or 'w'. Use it to catch a command output ('r' mode) or to feed it ('w' mode).
remove(path) | See unlink.
rename(src, dst) | Renames/moves the file or directory src to dst. [error if target name already exists]
rmdir(path) | Removes the empty directory path
read(fd, n) | Reads n bytes from file descriptor fd and return as string.
stat(path) | Returns st_mode, st_ino, st_dev, st_nlink, st_uid,st_gid, st_size, st_atime, st_mtime, st_ctime. [st_ino, st_uid, st_gid are dummy on Windows]
system(command) | Executes string command in a subshell. Returns exit status of subshell (usually 0 means OK).
times() | Returns accumulated CPU times in sec (user, system, children's user,children's sys, elapsed real time). [3 last not on Windows]
unlink(path) | Unlinks ("deletes") the file (not dir!) path. same as: remove
utime(path, (aTime, mTime)) | Sets the access & modified time of the file to the given tuple of values.
wait() | Waits for child process completion. Returns tuple ofpid, exit_status [Not on Windows]
waitpid(pid, options) | Waits for process pid to complete. Returns tuple ofpid, exit_status [Not on Windows]
write(fd, str) | Writes str to file fd. Returns nb of bytes written.

posixpath
Do not import this module directly, import os instead and refer to this module as os.path. (e.g. os.path.exists(p)) !

Some posixpath functions
Function | Result
--- | ---
abspath(p) | Returns absolute path for path p, taking current working dir in account.
dirname/basename(p) | directory and name parts of the path p. See also split.
exists(p) | True if string p is an existing path (file or directory)
expanduser(p) | Returns string that is (a copy of) p with "~" expansion done.
expandvars(p) | Returns string that is (a copy of) p with environment vars expanded. [Windows: case significant; must use Unix: $var notation, not %var%]
getsize(filename) | return the size in bytes of filename. raise os.error.
getmtime(filename) | return last modification time of filename (integer nb of seconds since epoch).
getatime(filename) | return last access time of filename (integer nb of seconds since epoch).
isabs(p) | True if string p is an absolute path.
isdir(p) | True if string p is a directory.
islink(p) | True if string p is a symbolic link.
ismount(p) | True if string p is a mount point [true for all dirs on Windows].
join(p[,q[,...]]) | Joins one or more path components intelligently.
split(p) | Splits p into (head, tail) where tail is last pathname component and <head> is everything leading up to that. <=> (dirname(p), basename(p))
splitdrive(p) | Splits path p in a pair ('drive:', tail) [Windows]
splitext(p) | Splits into (root, ext) where last comp of root contains no periods and ext is empty or starts with a period.
walk(p, visit, arg) | Calls the function visit with arguments(arg, dirname, names) for each directory recursively in the directory tree rooted at p (including p itself if it's a dir.) The argument dirname specifies the visited directory, the argument names lists the files in the directory. The visit function may modify names to influence the set of directories visited belowdirname, e.g., to avoid visiting certain parts of the tree.

shutil
high-level file operations (copying, deleting).

Main shutil functions
Function | Result
--- | ---
copy(src, dst) | Copies the contents of file src to file dst, retaining file permissions.
copytree(src, dst[, symlinks]) | Recursively copies an entire directory tree rooted at srcinto dst (which should not already exist). If symlinks is true, links insrc are kept as such in dst.
rmtree(path[, ignore_errors[, onerror]]) | Deletes an entire directory tree, ignoring errors if ignore_errors true,or calling onerror(func, path, sys.exc_info()) if supplied with func: faulty function, path: concerned file.

(and also: copyfile, copymode, copystat, copy2)

time

Variables
Variable | Meaning
--- | ---
altzone | signed offset of local DST timezone in sec west of the 0th meridian.
daylight | nonzero if a DST timezone is specified

Functions
Function | Result
--- | ---
time() | return a float representing UTC time in seconds since the epoch.
gmtime(secs), localtime(secs) | return a tuple representing time : (year aaaa, month(1-12),day(1-31), hour(0-23), minute(0-59), second(0-59), weekday(0-6, 0 is monday), Julian day(1-366), daylight flag(-1,0 or 1))
asctime(timeTuple), |
strftime(format, timeTuple) | return a formated string representing time.
mktime(tuple) | inverse of localtime(). Return a float.
strptime(string[, format]) | parse a formated string representing time, return tuple as in gmtime().
sleep(secs) | Suspend execution for <secs> seconds. <secs> can be a float.

and also: clock, ctime.

string
As of Python 2.0, much (though not all) of the functionality provided by the string module have been superseded by built-in string methods - see Operations on strings for details.

Some string variables
Variable | Meaning
--- | ---
digits | The string '0123456789'
hexdigits, octdigits | legal hexadecimal & octal digits
letters, uppercase, lowercase, whitespace | Strings containing the appropriate characters
index_error | Exception raised by index() if substr not found.

Some string functions
Function | Result
--- | ---
expandtabs(s, tabSize) | returns a copy of string <s> with tabs expanded.
find/rfind(s, sub[, start=0[, end=0]) | Return the lowest/highest index in <s> where the substring <sub> is found such that <sub> is wholly contained in s[start:end]. Return -1 if <sub> not found.
ljust/rjust/center(s, width) | Return a copy of string <s> left/right justified/centerd in a field of given width, padded with spaces. <s> is never truncated.
lower/upper(s) | Return a string that is (a copy of) <s> in lowercase/uppercase
split(s[, sep=whitespace[, maxsplit=0]]) | Return a list containing the words of the string <s>,using the string <sep> as a separator.
join(words[, sep=' ']) | Concatenate a list or tuple of words with intervening separators; inverse of split.
replace(s, old, new[, maxsplit=0] | Returns a copy of string <s> with all occurences of substring<old> replaced by <new>. Limits to <maxsplit> first substitutions if specified.
strip(s) | Return a string that is (a copy of) <s> without leading and trailing whitespace. see also lstrip, rstrip.

re (sre)

Handles Unicode strings. Implemented in new module sre, re now a mere front-end for compatibility.
Patterns are specified as strings. Tip: Use raw strings (e.g. r'\w*') to litteralize backslashes.

Regular expression syntax
Form | Description
--- | ---
. | matches any character (including newline if DOTALL flag specified)
^ | matches start of the string (of every line in MULTILINE mode)
$ | matches end of the string (of every line in MULTILINE mode)
* | 0 or more of preceding regular expression (as many as possible)
+ | 1 or more of preceding regular expression (as many as possible)
? | 0 or 1 occurence of preceding regular expression
*?, +?, ?? | Same as *, + and ? but matches as few characters as possible
{m,n} | matches from m to n repetitions of preceding RE
{m,n}? | idem, attempting to match as few repetitions as possible
[ ] | defines character set: e.g. '[a-zA-Z]' to match all letters (see also \w \S)
[^ ] | defines complemented character set: matches if char is NOT in set
\ | escapes special chars '*?+&$|()' and introduces special sequences (see below). Due to Python string rules, write as '\\' or r'\' in the pattern string.
\\ | matches a litteral '\'; due to Python string rules, write as '\\\\' in pattern string, or better using raw string: r'\\'.
| | specifies alternative: 'foo|bar' matches 'foo' or 'bar'
(...) | matches any RE inside (), and delimits a group.
(?:...) | idem but doesn't delimit a group.
(?=...) | matches if ... matches next, but doesn't consume any of the string e.g. 'Isaac (?=Asimov)' matches 'Isaac' only if followed by 'Asimov'.
(?!...) | matches if ... doesn't match next. Negative of (?=...)
(?P<name>...) | matches any RE inside (), and delimits a named group. (e.g. r'(?P<id>[a-zA-Z_]\w*)' defines a group named id)
(?P=name) | matches whatever text was matched by the earlier group named name.
(?#...) | A comment; ignored.
(?letter) | letter is one of 'i','L', 'm', 's', 'x'. Set the corresponding flags (re.I, re.L, re.M, re.S, re.X) for the entire RE.

Special sequences
Sequence | Description
--- | ---
number | matches content of the group of the same number; groups are numbered starting from 1
\A | matches only at the start of the string
\b | empty str at beg or end of word: '\bis\b' matches 'is', but not 'his'
\B | empty str NOT at beginning or end of word
\d | any decimal digit (<=> [0-9])
\D | any non-decimal digit char (<=> [^O-9])
\s | any whitespace char (<=> [ \t\n\r\f\v])
\S | any non-whitespace char (<=> [^ \t\n\r\f\v])
\w | any alphaNumeric char (depends on LOCALE flag)
\W | any non-alphaNumeric char (depends on LOCALE flag)
\Z | matches only at the end of the string

Variables
Variable | Meaning
--- | ---
error | Exception when pattern string isn't a valid regexp.

Functions
Function | Result
--- | ---
compile(pattern[, flags=0]) | Compile a RE pattern string into a regular expression object. Flags (combinable by |): I or IGNORECASE or (?i) case insensitive matching L or LOCALE or (?L) make \w, \W, \b, \B dependent on thecurrent locale M or MULTILINE or (?m) matches every new line and not onlystart/end of the whole string S or DOTALL or (?s) '.' matches ALL chars, including newline X or VERBOSE or (?x) Ignores whitespace outside character sets
escape(string) | return (a copy of) string with all non-alphanumerics backslashed.
match(pattern, string[, flags]) | if 0 or more chars at beginning of <string> match the RE pattern string,return a corresponding MatchObject instance, or None if no match.
search(pattern, string[, flags]) | scan thru <string> for a location matching <pattern>, return a corresponding MatchObject instance, or None if no match.
split(pattern, string[, maxsplit=0]) | split <string> by occurrences of <pattern>. If capturing () are used in pattern, then occurrences of patterns or subpatterns are also returned.
findall(pattern, string) | return a list of non-overlapping matches in <pattern>, either a list of groups or a list of tuples if the pattern has more than 1 group.
sub(pattern, repl, string[, count=0]) | return string obtained by replacing the (<count> first) leftmost non-overlapping occurrences of <pattern> (a string or a RE object) in <string> by <repl>; <repl> can be a string or a function called with a single MatchObj arg, which must return the replacement string.
subn(pattern, repl, string[, count=0]) | same as sub(), but returns a tuple (newString, numberOfSubsMade)

## Regular Expression Objects

(RE objects are returned by the compile fct)

re object attributes
Attribute | Descrition
--- | ---
flags | flags arg used when RE obj was compiled, or 0 if none provided
groupindex | dictionary of {group name: group number} in pattern
pattern | pattern string from which RE obj was compiled

re object methods
Method | Result
--- | ---
match(string[, pos][, endpos]) | If zero or more characters at the beginning of string match this regular expression, return a corresponding MatchObject instance. Return None if the string does not match the pattern; note that this is different from a zero-length match. The optional second parameter pos gives an index in the string where the search is to start; it defaults to 0. This is not completely equivalent to slicing the string; the '' pattern character matches at the real beginning of the string and at positions just after a newline, but not necessarily at the index where the search is to start. The optional parameter endpos limits how far the string will be searched; it will be as if the string is endpos characters long, so only the characters from pos to endpos will be searched for a match.
search(string[, pos][, endpos]) | Scan through string looking for a location where this regular expression produces a match, and return a corresponding MatchObject instance. Return None if no position in the string matches the pattern; note that this is different from finding a zero-length match at some point in the string. The optional pos and endpos parameters have the same meaning as for the match() method.
split(string[, maxsplit=0]) | Identical to the split() function, using the compiled pattern.
findall(string) | Identical to the findall() function, using the compiled pattern.
sub(repl, string[, count=0]) | Identical to the sub() function, using the compiled pattern.
subn(repl, string[, count=0]) | Identical to the subn() function, using the compiled pattern.

## Match Objects

(Match objects are returned by the match & search functions)

Match object attributes
Attribute | Description
--- | ---
pos | value of pos passed to search or match functions; index into string at which RE engine started search.
endpos | value of endpos passed to search or match functions; index into string beyond which RE engine won't go.
re | RE object whose match or search fct produced this MatchObj instance
string | string passed to match() or search()

Match object functions
Function | Result
--- | ---
group([g1, g2, ...]) | returns one or more groups of the match. If one arg, result is a string; if multiple args, result is a tuple with one item per arg. If gi is 0, return value is entire matching string; if 1 <= gi <= 99, return string matching group #gi (or None if no such group); gi may also be a group name.
groups() | returns a tuple of all groups of the match; groups not participating to the match have a value of None. Returns a string instead of tupleif len(tuple)=1
start(group), end(group) | returns indices of start & end of substring matched by group (or None if group exists but doesn't contribute to the match)
span(group) | returns the 2-tuple (start(group), end(group)); can be (None, None) if group didn't contibute to the match.

math

Variables:

    pi
    e

Functions (see ordinary C man pages for info):

    acos(x)
    asin(x)
    atan(x)
    atan2(x, y)
    ceil(x)
    cos(x)
    cosh(x)
    exp(x)
    fabs(x)
    floor(x)
    fmod(x, y)
    frexp(x)        -- Unlike C: (float, int) = frexp(float)
    ldexp(x, y)
    log(x)
    log10(x)
    modf(x)         -- Unlike C: (float, float) = modf(float)
    pow(x, y)
    sin(x)
    sinh(x)
    sqrt(x)
    tan(x)
    tanh(x)

getopt

Functions:

    getopt(list, optstr)    -- Similar to C. <optstr> is option
                               letters to look for. Put ':' after letter
                               if option takes arg. E.g.
        # invocation was "python test.py -c hi -a arg1 arg2"
           opts, args =  getopt.getopt(sys.argv[1:], 'ab:c:')
        # opts would be
           [('-c', 'hi'), ('-a', '')]
        # args would be
           ['arg1', 'arg2']

## List of modules and packages in base distribution

### (built-ins and content of python Lib directory)
(Python NT distribution, may be slightly different in other distributions)

Standard library modules
Operation | Result
--- | ---
aifc | Stuff to parse AIFF-C and AIFF files.
anydbm | Generic interface to all dbm clones. (dbhash, gdbm, dbm,dumbdbm)
asynchat | Support for 'chat' style protocols
asyncore | Asynchronous File I/O (in select style)
atexit | Register functions to be called at exit of Python interpreter.
audiodev | Audio support for a few platforms.
base64 | Conversions to/from base64 RFC-MIME transport encoding .
BaseHTTPServer | Base class forhttp services.
Bastion | "Bastionification" utility (control access to instance vars)
bdb | A generic Python debugger base class.
binhex | Macintosh binhex compression/decompression.
bisect | List bisection algorithms.
calendar | Calendar printing functions.
cgi | Wraps the WWW Forms Common Gateway Interface (CGI).
CGIHTTPServer | CGI http services.
cmd | A generic class to build line-oriented command interpreters.
cmp | Efficiently compare files, boolean outcome only.
cmpcache | Same, but caches 'stat' results for speed.
code | Utilities needed to emulate Python's interactive interpreter
codecs | Lookup existing Unicode encodings and register new ones.
colorsys | Conversion functions between RGB and other color systems.
commands | Tools for executing UNIX commands .
compileall | Force "compilation" of all .py files in a directory.
ConfigParser | Configuration file parser (much like windows .ini files)
copy | Generic shallow and deep copying operations.
copy_reg | Helper to provide extensibility for pickle/cPickle.
dbhash | (g)dbm-compatible interface to bsdhash.hashopen.
difflib | Tool for comparing sequences, and computing the changes required to convert one into another.
dircache | Sorted list of files in a dir, using a cache.
dircmp | Defines a class to build directory diff tools on.
dis | Bytecode disassembler.
distutils | Package installation system.
doctest | Unit testing framework based on running examples embedded in docstrings.
dospath | Common operations on DOS pathnames.
dumbdbm | A dumb and slow but simple dbm clone.
dump | Print python code that reconstructs a variable.
exceptions | Class based built-in exception hierarchy.
filecmp | File comparison.
fileinput | Helper class to quickly write a loop over all standard input files.
find | Find files directory hierarchy matching a pattern.
fnmatch | Filename matching with shell patterns.
formatter | A test formatter.
fpformat | General floating point formatting functions.
ftplib | An FTP client class. Based on RFC 959.
gc | Perform garbacge collection, obtain GC debug stats, and tune GC parameters.
getopt | Standard command line processing. See also ftp://www.pauahtun.org/pub/getargspy.zip
getpass | Utilities to get a password and/or the current user name.
glob | filename globbing.
gopherlib | Gopher protocol client interface.
grep | 'grep' utilities.
gzip | Read & write gzipped files.
htmlentitydefs | Proposed entity definitions for HTML.
htmllib | HTML parsing utilities.
httplib | HTTP client class.
ihooks | Hooks into the "import" mechanism.
imaplib | IMAP4 client.Based on RFC 2060.
imghdr | Recognizing image files based on their first few bytes.
imputil | Privides a way of writing customised import hooks.
inspect | Get information about live Python objects.
keyword | List of Python keywords.
knee | A Python re-implementation of hierarchical module import.
linecache | Cache lines from files.
linuxaudiodev | Linux /dev/audio support.
locale | Support for number formatting using the current locale settings.
macpath | Pathname (or related) operations for the Macintosh.
macurl2path | Mac specific module for conversion between pathnames and URLs.
mailbox | A class to handle a unix-style or mmdf-style mailbox.
mailcap | Mailcap file handling (RFC 1524).
mhlib | MH (mailbox) interface.
mimetools | Various tools used by MIME-reading or MIME-writing programs.
mimetypes | Guess the MIME type of a file.
MimeWriter | Generic MIME writer.
mimify | Mimification and unmimification of mail messages.
mmap | Interface to memory-mapped files - they behave like mutable strings.
multifile | Class to make multi-file messages easier to handle.
mutex | Mutual exclusion -- for use with module sched.
netrc | parses and encapsulates the netrc file format
nntplib | An NNTP client class. Based on RFC 977.
ntpath | Common operations on DOS pathnames.
nturl2path | Mac specific module for conversion between pathnames and URLs.
os | Either mac, dos or posix depending system.
packmail | Create a self-unpacking shell archive.
pdb | A Python debugger.
pickle | Pickling (save and restore) of Python objects (a faster Cimplementation exists in built-in module: cPickle).
pipes | Conversion pipeline templates.
poly | Polynomials.
popen2 | variations on pipe open.
poplib | A POP3 client class. Based on the J. Myers POP3 draft.
posixfile | Extended (posix) file operations.
posixpath | Common operations on POSIX pathnames.
pprint | Support to pretty-print lists, tuples, & dictionaries recursively.
profile | Class for profiling python code.
pstats | Class for printing reports on profiled python code.
pty | Pseudo terminal utilities.
py_compile | Routine to "compile" a .py file to a .pyc file.
pyclbr | Parse a Python file and retrieve classes and methods.
pydoc | Interactively convert docstrings to HTML or text.
pyexpat | Interface to the Expay XML parser.
PyUnit | Unit test framework inspired by JUnit.
Queue | A multi-producer, multi-consumer queue.
quopri | Conversions to/from quoted-printable transport encoding.
rand | Don't use unless you want compatibility with C's rand().
random | Random variable generators (obsolete, use whrandom)
re | Regular Expressions.
reconvert | Convert old ("regex") regular expressions to new syntax ("re").
regex_syntax | Flags for regex.set_syntax().
regexp | Backward compatibility for module "regexp" using "regex".
regsub | Regular expression subroutines.
repr | Redo repr() but with limits on most sizes.
rexec | Restricted execution facilities ("safe" exec, eval, etc).
rfc822 | RFC-822 message manipulation class.
rlcompleter | Word completion for GNU readline 2.0.
robotparser | Parse robot.txt files, useful for web spiders.
sched | A generally useful event scheduler class.
sgmllib | A parser for SGML.
shelve | Manage shelves of pickled objects.
shlex | Lexical analyzer class for simple shell-like syntaxes.
shutil | Utility functions usable in a shell-like program.
SimpleHTTPServer | Simple extension to base http class
site | Append module search paths for third-party packages to sys.path.
smtplib | SMTP Client class (RFC 821)
sndhdr | Several routines that help recognizing sound.
SocketServer | Generic socket server classes.
stat | Constants and functions for interpreting stat/lstat struct.
statcache | Maintain a cache of file stats.
statvfs | Constants for interpreting statvfs struct as returned by os.statvfs() and os.fstatvfs() (if they exist).
string | A collection of string operations.
StringIO | File-like objects that read/write a string buffer (a faster C implementation exists in built-in module: cStringIO).
sunau | Stuff to parse Sun and NeXT audio files.
sunaudio | Interpret sun audio headers.
symbol | Non-terminal symbols of Python grammar (from "graminit.h").
tabnanny | Check Python source for ambiguous indentation.
telnetlib | TELNET client class. Based on RFC 854.
tempfile | Temporary file name allocation.
threading | Proposed new higher-level threading interfaces
threading_api | (doc of the threading module)
toaiff | Convert "arbitrary" sound files to AIFF files .
token | Tokens (from "token.h").
tokenize | Compiles a regular expression that recognizes Python tokens.
traceback | Format and print Python stack traces.
tty | Terminal utilities.
turtle | LogoMation-like turtle graphics
types | Define names for all type symbols in the std interpreter.
tzparse | Parse a timezone specification.
unicodedata | Interface to unicode properties.
urllib | Open an arbitrary URL.
urlparse | Parse URLs according to latest draft of standard.
user | Hook to allow user-specified customization code to run.
UserDict | A wrapper to allow subclassing of built-in dict class.
UserList | A wrapper to allow subclassing of built-in list class.
UserString | A wrapper to allow subclassing of built-in string class.
util | some useful functions that don't fit elsewhere !!
uu | UUencode/UUdecode.
warnings | Issue warnings, and filter unwanted warnings.
wave | Stuff to parse WAVE files.
weakref | Allows the creation of object references which do not force the object to remain extant. Also allows the creation of proxy objects.
webbrowser | Platform independent URL launcher.
whatsound | Several routines that help recognizing sound files.
whichdb | Guess which db package to use to open a db file.
whrandom | Wichmann-Hill random number generator.
xdrlib | Implements (a subset of) Sun XDR (eXternal Data Representation)
xmllib | A parser for XML, using the derived class as static DTD.
xml.dom | Classes for processing XML using the Document Object Model.
xml.sax | Classes for processing XML using the SAX API.
xreadlines | Provides a sequence-like object for reading a file line-by-line without reading the entire file into memory.
zipfile | Read & write PK zipped files.
zmod | Demonstration of abstruse mathematical concepts.

### (following list not revised)
* Built-ins *

                sys                 Interpreter state vars and functions
                __built-in__        Access to all built-in python identifiers
                __main__            Scope of the interpreters main program, script or stdin
                array               Obj efficiently representing arrays of basic values
                math                Math functions of C standard
                time                Time-related functions
                regex               Regular expression matching operations
                marshal             Read and write some python values in binary format
                struct              Convert between python values and C structs

### * Standard *

                getopt              Parse cmd line args in sys.argv.  A la UNIX 'getopt'.
                os                  A more portable interface to OS dependent functionality
                re                  Functions useful for working with regular expressions
                string              Useful string and characters functions and exceptions
                whrandom            Wichmann-Hill pseudo-random number generator
                thread              Low-level primitives for working with process threads
                threading           idem, new recommanded interface.

### * Unix/Posix *

                dbm                 Interface to Unix ndbm database library
                grp                 Interface to Unix group database
                posix               OS functionality standardized by C and POSIX standards
                posixpath           POSIX pathname functions
                pwd                 Access to the Unix password database
                select              Access to Unix select multiplex file synchronization
                socket              Access to BSD socket interface

### * Tk User-interface Toolkit *

                tkinter             Main interface to Tk

### * Multimedia *

                audioop             Useful operations on sound fragments
                imageop             Useful operations on images
                jpeg                Access to jpeg image compressor and decompressor
                rgbimg              Access SGI imglib image files

### * Cryptographic Extensions *

                md5                 Interface to RSA's MD5 message digest algorithm
                mpz                 Interface to int part of GNU multiple precision library
                rotor               Implementation of a rotor-based encryption algorithm

### * Stdwin * Standard Window System

                stdwin              Standard Window System interface
                stdwinevents        Stdwin event, command, and selection constants
                rect                Rectangle manipulation operations

### * SGI IRIX * (4 & 5)

                al          SGI audio facilities
                AL          al constants
                fl          Interface to FORMS library
                FL          fl constants
                flp Functions for form designer
                fm          Access to font manager library
                gl          Access to graphics library
                GL          Constants for gl
                DEVICE      More constants for gl
                imgfile     Imglib image file interface

### * Suns *

                sunaudiodev Access to sun audio interface

## Workspace exploration and idiom hints

            dir(<module>)                                list functions, variables in <module>
            dir();                                       get object keys, defaults to local name space
            X.__methods__;                               list of methods supported by X (if any)
            X.__members__                                List of X's data attributes
            if __name__ == '__main__': main()            invoke main if running as script
            map(None, lst1, lst2, ...)                   merge lists
            b = a[:]                                     create copy of seq structure
            _                                            in interactive mode, is last value printed

## Python Mode for Emacs

    (Not revised, possibly not up to date)

    Type C-c ? when in python-mode for extensive help.
    INDENTATION
    Primarily for entering new code:
            TAB      indent line appropriately
            LFD      insert newline, then indent
            DEL      reduce indentation, or delete single character
    Primarily for reindenting existing code:
            C-c :    guess py-indent-offset from file content; change locally
            C-u C-c :        ditto, but change globally
            C-c TAB  reindent region to match its context
            C-c <    shift region left by py-indent-offset
            C-c >    shift region right by py-indent-offset
    MARKING & MANIPULATING REGIONS OF CODE
    C-c C-b         mark block of lines
    M-C-h           mark smallest enclosing def
    C-u M-C-h       mark smallest enclosing class
    C-c #           comment out region of code
    C-u C-c #       uncomment region of code
    MOVING POINT
    C-c C-p         move to statement preceding point
    C-c C-n         move to statement following point
    C-c C-u         move up to start of current block
    M-C-a           move to start of def
    C-u M-C-a       move to start of class
    M-C-e           move to end of def
    C-u M-C-e       move to end of class
    EXECUTING PYTHON CODE
    C-c C-c sends the entire buffer to the Python interpreter
    C-c |   sends the current region
    C-c !   starts a Python interpreter window; this will be used by
            subsequent C-c C-c or C-c | commands
    VARIABLES
    py-indent-offset        indentation increment
    py-block-comment-prefix comment string used by py-comment-region
    py-python-command       shell command to invoke Python interpreter
    py-scroll-process-buffer        t means always scroll Python process buffer
    py-temp-directory       directory used for temp files (if needed)
    py-beep-if-tab-change   ring the bell if tab-width is changed

## The Python Debugger

    (Not revised, possibly not up to date, see 1.5.2 Library Ref section 9.1; in 1.5.2, you may also use debugger integrated in IDLE)

### Accessing

    import pdb      (it's a module written in Python)
            -- defines functions :
               run(statement[,globals[, locals]])
                            -- execute statement string under debugger control, with optional
                               global & local environment.
               runeval(expression[,globals[, locals]])
                            -- same as run, but evaluate expression and return value.
               runcall(function[, argument, ...])
                            -- run function object with given arg(s)
               pm()         -- run postmortem on last exception (like debugging a core file)
               post_mortem(t)
                            -- run postmortem on traceback object <t>

            -- defines class Pdb :
               use Pdb to create reusable debugger objects. Object
               preserves state (i.e. break points) between calls.

            runs until a breakpoint hit, exception, or end of program
            If exception, variable '__exception__' holds (exception,value).

### Commands

    h, help
            brief reminder of commands
    b, break [<arg>]
            if <arg> numeric, break at line <arg> in current file
            if <arg> is function object, break on entry to function <arg>
            if no arg, list breakpoints
    cl, clear [<arg>]
            if <arg> numeric, clear breakpoint at <arg> in current file
            if no arg, clear all breakpoints after confirmation
    w, where
            print current call stack
    u, up
            move up one stack frame (to top-level caller)
    d, down
            move down one stack frame
    s, step
            advance one line in the program, stepping into calls
    n, next
            advance one line, stepping over calls
    r, return
            continue execution until current function returns
            (return value is saved in variable "__return__", which
            can be printed or manipulated from debugger)
    c, continue
            continue until next breakpoint
    a, args
            print args to current function
    rv, retval
            prints return value from last function that returned
    p, print <arg>
            prints value of <arg> in current stack frame
    l, list [<first> [, <last>]]
                   List source code for the current file.
                   Without arguments, list 11 lines around the current line
                   or continue the previous listing.
                   With one argument, list 11 lines starting at that line.
                   With two arguments, list the given range;
                   if the second argument is less than the first, it is a count.
    whatis <arg>
            prints type of <arg>
    !
            executes rest of line as a Python statement in the current stack frame
    q quit
            immediately stop execution and leave debugger
    <return>
            executes last command again
    Any input debugger doesn't recognize as a command is assumed to be a
    Python statement to execute in the current stack frame, the same way
    the exclamation mark ("!") command does.

### Example

    (1394) python
    Python 1.0.3 (Sep 26 1994)
    Copyright 1991-1994 Stichting Mathematisch Centrum, Amsterdam
    >>> import rm
    >>> rm.run()
    Traceback (innermost last):
             File "<stdin>", line 1
             File "./rm.py", line 7
               x = div(3)
             File "./rm.py", line 2
               return a / r
    ZeroDivisionError: integer division or modulo
    >>> import pdb
    >>> pdb.pm()
    > ./rm.py(2)div: return a / r
    (Pdb) list
             1     def div(a):
             2  ->     return a / r
             3
             4     def run():
             5         global r
             6         r = 0
             7         x = div(3)
             8         print x
    [EOF]
    (Pdb) print r
    0
    (Pdb) q
    >>> pdb.runcall(rm.run)
    etc.

### Quirks

Breakpoints are stored as filename, line number tuples. If a module is reloaded after editing, any remembered breakpoints are likely to be wrong.

Always single-steps through top-most stack frame. That is, "c" acts like "n".