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.TH PYTHON "1"

.\" To view this file while editing, run it through groff:

.\" groff -Tascii -man python.man | less

.SH NAME

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

.SH SYNOPSIS

.B python

[

.B \-B

]

[

.B \-d

]

[

.B \-E

]

[

.B \-h

]

[

.B \-i

]

[

.B \-m

.I module-name

]

.br

[

.B \-O

]

[

.B \-OO

]

[

.B \-R

]

[

.B -Q

.I argument

]

[

.B \-s

]

[

.B \-S

]

[

.B \-t

]

[

.B \-u

]

.br

[

.B \-v

]

[

.B \-V

]

[

.B \-W

.I argument

]

[

.B \-x

]

[

.B \-3

]

[

.B \-?

]

.br

[

.B \-c

.I command

.I script

]

[

.I arguments

]

.SH 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, see 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

.B "INTERNET RESOURCES"

below; they may be installed on your system as well.)

.PP

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.

.PP

Documentation for installed Python modules and packages can be

viewed by running the

.B pydoc

program.

.SH COMMAND LINE OPTIONS

.TP

.B \-B

Don't write

.I .py[co]

files on import. See also PYTHONDONTWRITEBYTECODE.

.TP

.BI "\-c " command

Specify the command to execute (see next section).

This terminates the option list (following options are passed as

arguments to the command).

.TP

.B \-d

Turn on parser debugging output (for wizards only, depending on

compilation options).

.TP

.B \-E

Ignore environment variables like PYTHONPATH and PYTHONHOME that modify

the behavior of the interpreter.

.TP

.B \-h ", " \-? ", "\-\-help

Prints the usage for the interpreter executable and exits.

.TP

.B \-i

When a script is passed as first argument or the \fB\-c\fP 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.

.TP

.BI "\-m " module-name

Searches

.I sys.path

for the named module and runs the corresponding

.I .py

file as a script.

.TP

.B \-O

Turn on basic optimizations. This changes the filename extension for

compiled (bytecode) files from

.I .pyc

to \fI.pyo\fP. Given twice, causes docstrings to be discarded.

.TP

.B \-OO

Discard docstrings in addition to the \fB-O\fP optimizations.

.TP

.B \-R

Turn on "hash randomization", so that the hash() values of str, bytes and

datetime objects are "salted" with an unpredictable pseudo-random value.

Although they remain constant within an individual Python process, they are

not predictable between repeated invocations of Python.

.IP

This is intended to provide protection against a denial of service

caused by carefully-chosen inputs that exploit the worst case performance

of a dict construction, O(n^2) complexity. See

http://www.ocert.org/advisories/ocert-2011-003.html

for details.

.TP

.BI "\-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.

.TP

.B \-s

Don't add user site directory to sys.path.

.TP

.B \-S

Disable the import of the module

.I site

and the site-dependent manipulations of

.I sys.path

that it entails.

.TP

.B \-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.

.TP

.B \-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.

.TP

.B \-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.

.TP

.B \-V ", " \-\-version

Prints the Python version number of the executable and exits.

.TP

.BI "\-W " argument

Warning control. Python sometimes prints warning message to

.IR sys.stderr .

A typical warning message has the following form:

.IB 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

.B \-W

options may be given; when a warning matches more than one

option, the action for the last matching option is performed.

Invalid

.B \-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

.I warnings

module.

The simplest form of

.I argument

is one of the following

.I action

strings (or a unique abbreviation):

.B ignore

to ignore all warnings;

.B default

to explicitly request the default behavior (printing each warning once

per source line);

.B 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);

.B module

to print each warning only the first time it occurs in each

module;

.B once

to print each warning only the first time it occurs in the program; or

.B error

to raise an exception instead of printing a warning message.

The full form of

.I argument

.IB action : message : category : module : line.

Here,

.I 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

.I message

field matches the start of the warning message printed; this match is

case-insensitive. The

.I 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

.I module

field matches the (fully-qualified) module name; this match is

case-sensitive. The

.I line

field matches the line number, where zero matches all line numbers and

is thus equivalent to an omitted line number.

.TP

.B \-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!

.TP

.B \-3

Warn about Python 3.x incompatibilities that 2to3 cannot trivially fix.

.SH 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

.I script

from that file;

when called with

.B \-c

.IR command ,

it executes the Python statement(s) given as

.IR command .

Here

.I 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.

.PP

If available, the script name and additional arguments thereafter are

passed to the script in the Python variable

.IR sys.argv ,

which is a list of strings (you must first

.I import sys

to be able to access it).

If no script name is given,

.I sys.argv[0]

is an empty string; if

.B \-c

is used,

.I sys.argv[0]

contains the string

.I '-c'.

Note that options interpreted by the Python interpreter itself

are not placed in

.IR sys.argv .

.PP

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

.I sys.ps1

.IR 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

.I Keyboard\%Interrupt

exception; other UNIX signals are not caught (except that SIGPIPE is

sometimes ignored, in favor of the

.I IOError

exception). Error messages are written to stderr.

.SH 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.

The default for both is \fI/usr/local\fP.

.IP \fI${exec_prefix}/bin/python\fP

Recommended location of the interpreter.

.PP

.I ${prefix}/lib/python<version>

.br

.I ${exec_prefix}/lib/python<version>

.RS

Recommended locations of the directories containing the standard

modules.

.RE

.PP

.I ${prefix}/include/python<version>

.br

.I ${exec_prefix}/include/python<version>

.RS

Recommended locations of the directories containing the include files

needed for developing Python extensions and embedding the

interpreter.

.RE

.IP \fI~/.pythonrc.py\fP

User-specific initialization file loaded by the \fIuser\fP module;

not used by default or by most applications.

.SH ENVIRONMENT VARIABLES

.IP 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

\fI/usr/local\fP. 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}.

.IP 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

.IR sys.path .

.IP 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

.I sys.ps1

and

.I sys.ps2

in this file.

.IP PYTHONY2K

Set this to a non-empty string to cause the \fItime\fP module to

require dates specified as strings to include 4-digit years, otherwise

2-digit years are converted based on rules described in the \fItime\fP

module documentation.

.IP PYTHONOPTIMIZE

If this is set to a non-empty string it is equivalent to specifying

the \fB\-O\fP option. If set to an integer, it is equivalent to

specifying \fB\-O\fP multiple times.

.IP PYTHONDEBUG

If this is set to a non-empty string it is equivalent to specifying

the \fB\-d\fP option. If set to an integer, it is equivalent to

specifying \fB\-d\fP multiple times.

.IP PYTHONDONTWRITEBYTECODE

If this is set to a non-empty string it is equivalent to specifying

the \fB\-B\fP option (don't try to write

.I .py[co]

files).

.IP PYTHONINSPECT

If this is set to a non-empty string it is equivalent to specifying

the \fB\-i\fP option.

.IP PYTHONIOENCODING

If this is set before running the interpreter, it overrides the encoding used

for stdin/stdout/stderr, in the syntax

.IB encodingname ":" errorhandler

The

.IB errorhandler

part is optional and has the same meaning as in str.encode. For stderr, the

.IB errorhandler

part is ignored; the handler will always be \'backslashreplace\'.

.IP PYTHONNOUSERSITE

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

\fB\-s\fP option (Don't add the user site directory to sys.path).

.IP PYTHONUNBUFFERED

If this is set to a non-empty string it is equivalent to specifying

the \fB\-u\fP option.

.IP PYTHONVERBOSE

If this is set to a non-empty string it is equivalent to specifying

the \fB\-v\fP option. If set to an integer, it is equivalent to

specifying \fB\-v\fP multiple times.

.IP PYTHONWARNINGS

If this is set to a comma-separated string it is equivalent to

specifying the \fB\-W\fP option for each separate value.

.IP PYTHONHASHSEED

If this variable is set to "random", the effect is the same as specifying

the \fB-R\fP option: a random value is used to seed the hashes of str,

bytes and datetime objects.

If PYTHONHASHSEED is set to an integer value, it is used as a fixed seed for

generating the hash() of the types covered by the hash randomization. Its

purpose is to allow repeatable hashing, such as for selftests for the

interpreter itself, or to allow a cluster of python processes to share hash

values.

The integer must be a decimal number in the range [0,4294967295]. Specifying

the value 0 will lead to the same hash values as when hash randomization is

disabled.

.SH AUTHOR

The Python Software Foundation: https://www.python.org/psf/

.SH INTERNET RESOURCES

Main website: https://www.python.org/

.br

Documentation: https://docs.python.org/2/

.br

Developer resources: https://docs.python.org/devguide/

.br

Downloads: https://www.python.org/downloads/

.br

Module repository: https://pypi.python.org/

.br

Newsgroups: comp.lang.python, comp.lang.python.announce

.SH 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 otherwise using Python and for a

DISCLAIMER OF ALL WARRANTIES.

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