Python is an interpreted, interactive, object-oriented programming
language that combines remarkable power with very clear syntax.
For an introduction to programming in Python you are referred to the
Python Tutorial.
The Python Library Reference documents built-in and standard types,
constants, functions and modules.
Finally, the Python Reference Manual describes the syntax and
semantics of the core language in (perhaps too) much detail.
(These documents may be located via the
INTERNET RESOURCES
below; they may be installed on your system as well.)
Python's basic power can be extended with your own modules written in
C or C++.
On most systems such modules may be dynamically loaded.
Python is also adaptable as an extension language for existing
applications.
See the internal documentation for hints.
Documentation for installed Python modules and packages can be
viewed by running the
pydoc
program.
COMMAND LINE OPTIONS
-c command
Specify the command to execute (see next section).
This terminates the option list (following options are passed as
arguments to the command).
-d
Turn on parser debugging output (for wizards only, depending on
compilation options).
-E
Ignore environment variables like PYTHONPATH and PYTHONHOME that modify
the behavior of the interpreter.
-h
Prints the usage for the interpreter executable and exits.
-i
When a script is passed as first argument or the -c option is
used, enter interactive mode after executing the script or the
command. It does not read the $PYTHONSTARTUP file. This can be
useful to inspect global variables or a stack trace when a script
raises an exception.
-m module-name
Searches
sys.path
for the named module and runs the corresponding
.py
file as a script.
-O
Turn on basic optimizations. This changes the filename extension for
compiled (bytecode) files from
.pyc
to .pyo. Given twice, causes docstrings to be discarded.
-Q argument
Division control; see PEP 238. The argument must be one of "old" (the
default, int/int and long/long return an int or long), "new" (new
division semantics, i.e. int/int and long/long returns a float),
"warn" (old division semantics with a warning for int/int and
long/long), or "warnall" (old division semantics with a warning for
all use of the division operator). For a use of "warnall", see the
Tools/scripts/fixdiv.py script.
-S
Disable the import of the module
site
and the site-dependent manipulations of
sys.path
that it entails.
-t
Issue a warning when a source file mixes tabs and spaces for
indentation in a way that makes it depend on the worth of a tab
expressed in spaces. Issue an error when the option is given twice.
-u
Force stdin, stdout and stderr to be totally unbuffered. On systems
where it matters, also put stdin, stdout and stderr in binary mode.
Note that there is internal buffering in xreadlines(), readlines() and
file-object iterators ("for line in sys.stdin") which is not
influenced by this option. To work around this, you will want to use
"sys.stdin.readline()" inside a "while 1:" loop.
-v
Print a message each time a module is initialized, showing the place
(filename or built-in module) from which it is loaded. When given
twice, print a message for each file that is checked for when
searching for a module. Also provides information on module cleanup
at exit.
-V
Prints the Python version number of the executable and exits.
-W argument
Warning control. Python sometimes prints warning message to
sys.stderr.
A typical warning message has the following form:
file:line: category: message.
By default, each warning is printed once for each source line where it
occurs. This option controls how often warnings are printed.
Multiple
-W
options may be given; when a warning matches more than one
option, the action for the last matching option is performed.
Invalid
-W
options are ignored (a warning message is printed about invalid
options when the first warning is issued). Warnings can also be
controlled from within a Python program using the
warnings
module.
The simplest form of
argument
is one of the following
action
strings (or a unique abbreviation):
ignore
to ignore all warnings;
default
to explicitly request the default behavior (printing each warning once
per source line);
all
to print a warning each time it occurs (this may generate many
messages if a warning is triggered repeatedly for the same source
line, such as inside a loop);
module
to print each warning only only the first time it occurs in each
module;
once
to print each warning only the first time it occurs in the program; or
error
to raise an exception instead of printing a warning message.
The full form of
argument
is
action:message:category:module:line.
Here,
action
is as explained above but only applies to messages that match the
remaining fields. Empty fields match all values; trailing empty
fields may be omitted. The
message
field matches the start of the warning message printed; this match is
case-insensitive. The
category
field matches the warning category. This must be a class name; the
match test whether the actual warning category of the message is a
subclass of the specified warning category. The full class name must
be given. The
module
field matches the (fully-qualified) module name; this match is
case-sensitive. The
line
field matches the line number, where zero matches all line numbers and
is thus equivalent to an omitted line number.
-x
Skip the first line of the source. This is intended for a DOS
specific hack only. Warning: the line numbers in error messages will
be off by one!
INTERPRETER INTERFACE
The interpreter interface resembles that of the UNIX shell: when
called with standard input connected to a tty device, it prompts for
commands and executes them until an EOF is read; when called with a
file name argument or with a file as standard input, it reads and
executes a
script
from that file;
when called with
-ccommand,
it executes the Python statement(s) given as
command.
Here
command
may contain multiple statements separated by newlines.
Leading whitespace is significant in Python statements!
In non-interactive mode, the entire input is parsed before it is
executed.
If available, the script name and additional arguments thereafter are
passed to the script in the Python variable
sys.argv ,
which is a list of strings (you must first
import sys
to be able to access it).
If no script name is given,
sys.argv[0]
is an empty string; if
-c
is used,
sys.argv[0]
contains the string
'-c'.
Note that options interpreted by the Python interpreter itself
are not placed in
sys.argv.
In interactive mode, the primary prompt is `>>>'; the second prompt
(which appears when a command is not complete) is `...'.
The prompts can be changed by assignment to
sys.ps1
or
sys.ps2.
The interpreter quits when it reads an EOF at a prompt.
When an unhandled exception occurs, a stack trace is printed and
control returns to the primary prompt; in non-interactive mode, the
interpreter exits after printing the stack trace.
The interrupt signal raises the
KeyboardInterrupt
exception; other UNIX signals are not caught (except that SIGPIPE is
sometimes ignored, in favor of the
IOError
exception). Error messages are written to stderr.
FILES AND DIRECTORIES
These are subject to difference depending on local installation
conventions; ${prefix} and ${exec_prefix} are installation-dependent
and should be interpreted as for GNU software; they may be the same.
On Debian GNU/{Hurd,Linux} the default for both is /usr.
Recommended locations of the directories containing the include files
needed for developing Python extensions and embedding the
interpreter.
~/.pythonrc.py
User-specific initialization file loaded by the user module;
not used by default or by most applications.
ENVIRONMENT VARIABLES
PYTHONHOME
Change the location of the standard Python libraries. By default, the
libraries are searched in ${prefix}/lib/python<version> and
${exec_prefix}/lib/python<version>, where ${prefix} and ${exec_prefix}
are installation-dependent directories, both defaulting to
/usr/local. When $PYTHONHOME is set to a single directory, its value
replaces both ${prefix} and ${exec_prefix}. To specify different values
for these, set $PYTHONHOME to ${prefix}:${exec_prefix}.
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 colons.
Non-existent directories are silently ignored.
The default search path is installation dependent, but generally
begins with ${prefix}/lib/python<version> (see PYTHONHOME above).
The default search path is always appended to $PYTHONPATH.
If a script argument is given, the directory containing the script is
inserted in the path in front of $PYTHONPATH.
The search path can be manipulated from within a Python program as the
variable
sys.path .
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.
The file is executed in the same name space where interactive commands
are executed so that objects defined or imported in it can be used
without qualification in the interactive session.
You can also change the prompts
sys.ps1
and
sys.ps2
in this file.
PYTHONY2K
Set this to a non-empty string to cause the time module to
require dates specified as strings to include 4-digit years, otherwise
2-digit years are converted based on rules described in the time
module documentation.
PYTHONOPTIMIZE
If this is set to a non-empty string it is equivalent to specifying
the -O option. If set to an integer, it is equivalent to
specifying -O multiple times.
PYTHONDEBUG
If this is set to a non-empty string it is equivalent to specifying
the -d option. If set to an integer, it is equivalent to
specifying -d multiple times.
PYTHONINSPECT
If this is set to a non-empty string it is equivalent to specifying
the -i option.
PYTHONUNBUFFERED
If this is set to a non-empty string it is equivalent to specifying
the -u option.
PYTHONVERBOSE
If this is set to a non-empty string it is equivalent to specifying
the -v option. If set to an integer, it is equivalent to
specifying -v multiple times.
Python is distributed under an Open Source license. See the file
"LICENSE" in the Python source distribution for information on terms &
conditions for accessing and otherwise using Python and for a
DISCLAIMER OF ALL WARRANTIES.
