python - an interpreted, interactive, object-oriented programming language


python [ __-d__? [ __-i__? [ __-O__? __-S__? [ __-t__? [ __-u__? [ __-v__? __-x__? [ __-h__? [ __-V__? [ __-c__ ''command''? ''arguments''?


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.



Turn on parser debugging output (for wizards only, depending on compilation options).


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.


Turn on basic optimizations. This changes the filename extension for compiled (bytecode) files from .pyc to .pyo. Given twice, causes docstrings to be discarded.


Disable the import of the module site and the site-dependent manipulations of sys.path that it entails.


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.


Force stdin, stdout and stderr to be totally unbuffered.


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.


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!


Prints the usage for the interpreter executable and exits.


Prints the Python version number of the executable and exits.

-c command

Specify the command to execute (see next section). This terminates the option list (following options are passed as arguments to the command).


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 ` 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.


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. The default for both is /usr/local.


Recommended location of the interpreter.

${prefix}/lib/python ${exec_prefix}/lib/python''

Recommended locations of the directories containing the standard modules.

${prefix}/include/python ${exec_prefix}/include/python''

Recommended locations of the directories containing the include files needed for developing Python extensions and embedding the interpreter.


User-specific initialization file loaded by the user module; not used by default or by most applications.



Change the location of the standard Python libraries. By default, the libraries are searched in ${prefix}/lib/python /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}.


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 sys.path .''


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.


If this is set to a non-empty string it is equivalent to specifying the -d option.


If this is set to a non-empty string it is equivalent to specifying the -i option.


If this is set to a non-empty string it is equivalent to specifying the -u option.


If this is set to a non-empty string it is equivalent to specifying the -v option.


Guido van Rossum


160 Saratoga Avenue Santa Clara, CA 95051 USA E-mail:, And a cast of thousands.


Main website:

BeOpen? development team:

Community website: Developer resources: FTP: Module repository: Newsgroups: comp.lang.python, comp.lang.python.announce


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