PYTHON(1)PYTHON(1)NAME
python - an interpreted, interactive, object-oriented pro
gramming language
SYNOPSIS
python [ -d ] [ -i ] [ -O ] [ -S ] [ -t ] [ -u ] [ -v ] [
-x ] [ -h ] [ -V ] [ -W argument ]
[ -c command | script | - ] [ arguments ]
DESCRIPTION
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 exten
sion 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-d Turn on parser debugging output (for wizards only,
depending on compilation options).
-i When a script is passed as first argument or the -c
option is used, enter interactive mode after exe
cuting 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.
-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.
-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.
-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.
-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!
-h Prints the usage for the interpreter executable and
exits.
-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: mes_
sage. By default, each warning is printed once for
each source line where it occurs. This option con
trols 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). Warn
ings can also be controlled from within a Python
program using the warnings module.
The simplest form of argument is one of the follow
ing action strings (or a unique abbreviation):
ignore to ignore all warnings; default to explic
itly request the default behavior (printing each
warning once per source line); all to print a warn
ing each time it occurs (this may generate many
messages if a warning is triggered repeatedly for
the same source line, e.g. 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:cate_
gory: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 cate_
gory 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.
-c command
Specify the command to execute (see next section).
This terminates the option list (following options
are passed as arguments to the command).
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 -c command, 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
befored 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 sec
ond 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 instal
lation conventions; ${prefix} and ${exec_prefix} are
installation-dependent and should be interpreted as for
GNU software; they may be the same. The default for both
is /usr/local.
${exec_prefix}/bin/python
Recommended location of the interpreter.
${prefix}/lib/python<version>
${exec_prefix}/lib/python<version>
Recommended locations of the directories containing
the standard modules.
${prefix}/include/python<version>
${exec_prefix}/include/python<version>
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 appli
cations.
ENVIRONMENT VARIABLES
PYTHONHOME
Change the location of the standard Python
libraries. By default, the libraries are searched
in ${prefix}/lib/python<version> and ${exec_pre
fix}/lib/python<version>, where ${prefix} and
${exec_prefix} are installation-dependent directo
ries, both defaulting to /usr/local. When $PYTHON
HOME 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-
existant 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 argu
ment 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 interac
tive 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.
PYTHONDEBUG
If this is set to a non-empty string it is equiva
lent to specifying the -d option.
PYTHONINSPECT
If this is set to a non-empty string it is equiva
lent to specifying the -i option.
PYTHONUNBUFFERED
If this is set to a non-empty string it is equiva
lent to specifying the -u option.
PYTHONVERBOSE
If this is set to a non-empty string it is equiva
lent to specifying the -v option.
AUTHOR
Guido van Rossum
E-mail: guido@python.org
And a cast of thousands.
INTERNET RESOURCES
Main website: http://www.python.org
Community website: http://starship.python.net
Developer resources:
http://sourceforge.net/project/?group_id=5470
FTP: ftp://ftp.python.org/pub/python
Module repository: http://www.vex.net/parnassus/
Newsgroups: comp.lang.python, comp.lang.python.announce
LICENSING
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 other
wise using Python and for a DISCLAIMER OF ALL WARRANTIES.
5 September, 2000 PYTHON(1)
