Python 2.1 Quick Reference




 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, for Python 1.5.2 from V1.3 ref
1995/10/30, by Chris Hoffmann,

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,
    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,
    and the readers of comp.lang.python
Python's nest:
ActivePython :
newsgroup: comp.lang.python
Help desk:
Resources: and
Full documentation:
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.

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


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


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

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



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
not x boolean negation
x and y boolean and
x or y boolean or
Lowest lambda args: expr anonymous function

Basic Types and Their Operations

Comparisons (defined between *any* types)

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 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

Numeric exceptions

raised on application of arithmetic operation to non-number
 numeric bounds exceeded
 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. 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
        '%s has %03d quote types.' % ('Python', 2)  # => 'Python has 002 quote types.'
        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
Signed integer decimal. 
Signed integer decimal. 
Unsigned octal. 
Unsigned decimal. 
Unsigned hexidecimal (lowercase). 
Unsigned hexidecimal (uppercase). 
Floating point exponential format (lowercase). 
Floating point exponential format (uppercase). 
Floating point decimal format. 
Floating point decimal format. 
Same as "e" if exponent is greater than -4 or less than precision, "f" otherwise. 
Same as "E" if exponent is greater than -4 or less than precision, "F" otherwise. 
Single character (accepts integer or single character string). 
r  String (converts any python object using repr()). 
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''. 
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.[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.[, 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

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

Advanced Types

-See manuals for more details -


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

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

            class text_exception(Exception): pass
                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
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 ''
                (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;"
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;"
"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 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]
    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.
    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.
     class c (c_parent):
           def __init__(self, name): = name
           def print_name(self): print "I'm",
           def call_parent(self): c_parent.print_name(self)
           instance = c('tom')
           "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.
     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".


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:

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
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

         Root class for all exceptions
         On 'sys.exit()'
                 Base class for all built-in exceptions; derived from Exception root class.
                 Base class for OverflowError, ZeroDivisionError, FloatingPointError
                       When a floating point operation fails.

                        On excessively large arithmetic operation
              On division or modulo operation with 0 as 2nd arg

                When an assert statement fails.

                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.

                Immediate end-of-file hit by input() or raw_input()
     On failure of `import' to find module or name
     On user entry of the interrupt key (often `Control-C')
                base class for IndexError, KeyError
             On out-of-range sequence subscript
             On reference to a non-existent mapping (dict) key
     On recoverable memory exhaustion
     On failure to find a local or global (unqualified) name
     Obsolete catch-all; define a suitable error instead

      NotImplementedError   [new in 1.5.2]
            On method not implemented
     On parser encountering a syntax error

       On parser encountering an indentation syntax error

       On parser encountering an indentation syntax error

     On non-fatal interpreter error - bug - report it
     On passing inappropriate type to built-in op or func
     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 " = 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.


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)
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

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.

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)

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__'])

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

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

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)

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

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


Important Modules

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.)

"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
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.

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
_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.

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.

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)

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


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



Functions (see ordinary C man pages for info):
atan2(x, y)
fmod(x, y)
frexp(x)        -- Unlike C: (float, int) = frexp(float)
ldexp(x, y)
modf(x)         -- Unlike C: (float, float) = modf(float)
pow(x, y)


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 -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
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.
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
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
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
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
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)


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)
                        -- 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).


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
        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.


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


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".