Provided by: python3.8-minimal_3.8.10-0ubuntu1~20.04.18_amd64 
NAME
python - an interpreted, interactive, object-oriented programming language
SYNOPSIS
python [ -B ] [ -b ] [ -d ] [ -E ] [ -h ] [ -i ] [ -I ]
[ -m module-name ] [ -q ] [ -O ] [ -OO ] [ -s ] [ -S ] [ -u ]
[ -v ] [ -V ] [ -W argument ] [ -x ] [ [ -X option ] -? ]
[ --check-hash-based-pycs default | always | never ]
[ -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, 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 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
-B Don't write .pyc files on import. See also PYTHONDONTWRITEBYTECODE.
-b Issue warnings about str(bytes_instance), str(bytearray_instance) and comparing bytes/bytearray
with str. (-bb: issue errors)
-c command
Specify the command to execute (see next section). This terminates the option list (following
options are passed as arguments to the command).
--check-hash-based-pycs mode
Configure how Python evaluates the up-to-dateness of hash-based .pyc files.
-d Turn on parser debugging output (for expert only, depending on compilation options).
-E Ignore environment variables like PYTHONPATH and PYTHONHOME that modify the behavior of the
interpreter.
-h , -? , --help
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.
-I Run Python in isolated mode. This also implies -E and -s. In isolated mode sys.path contains
neither the script's directory nor the user's site-packages directory. All PYTHON* environment
variables are ignored, too. Further restrictions may be imposed to prevent the user from
injecting malicious code.
-m module-name
Searches sys.path for the named module and runs the corresponding .py file as a script.
-O Remove assert statements and any code conditional on the value of __debug__; augment the filename
for compiled (bytecode) files by adding .opt-1 before the .pyc extension.
-OO Do -O and also discard docstrings; change the filename for compiled (bytecode) files by adding
.opt-2 before the .pyc extension.
-q Do not print the version and copyright messages. These messages are also suppressed in non-
interactive mode.
-s Don't add user site directory to sys.path.
-S Disable the import of the module site and the site-dependent manipulations of sys.path that it
entails. Also disable these manipulations if site is explicitly imported later.
-u Force the stdout and stderr streams to be unbuffered. This option has no effect on the stdin
stream.
-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 , --version
Prints the Python version number of the executable and exits. When given twice, print more
information about the build.
-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 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 option
Set implementation specific option. The following options are available:
-X faulthandler: enable faulthandler
-X showrefcount: output the total reference count and number of used
memory blocks when the program finishes or after each statement in the
interactive interpreter. This only works on debug builds
-X tracemalloc: start tracing Python memory allocations using the
tracemalloc module. By default, only the most recent frame is stored in a
traceback of a trace. Use -X tracemalloc=NFRAME to start tracing with a
traceback limit of NFRAME frames
-X showalloccount: output the total count of allocated objects for each
type when the program finishes. This only works when Python was built with
COUNT_ALLOCS defined
-X importtime: show how long each import takes. It shows module name,
cumulative time (including nested imports) and self time (excluding
nested imports). Note that its output may be broken in multi-threaded
application. Typical usage is python3 -X importtime -c 'import asyncio'
-X dev: enable CPython's "development mode", introducing additional runtime
checks which are too expensive to be enabled by default. It will not be
more verbose than the default if the code is correct: new warnings are
only emitted when an issue is detected. Effect of the developer mode:
* Add default warning filter, as -W default
* Install debug hooks on memory allocators: see the PyMem_SetupDebugHooks() C function
* Enable the faulthandler module to dump the Python traceback on a crash
* Enable asyncio debug mode
* Set the dev_mode attribute of sys.flags to True
* io.IOBase destructor logs close() exceptions
-X utf8: enable UTF-8 mode for operating system interfaces, overriding the default
locale-aware mode. -X utf8=0 explicitly disables UTF-8 mode (even when it would
otherwise activate automatically). See PYTHONUTF8 for more details
-X pycache_prefix=PATH: enable writing .pyc files to a parallel tree rooted at the
given directory instead of to the code tree.
-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 -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 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.
${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.
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.
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.
PYTHONDONTWRITEBYTECODE
If this is set to a non-empty string it is equivalent to specifying the -B option (don't try to
write .pyc files).
PYTHONINSPECT
If this is set to a non-empty string it is equivalent to specifying the -i option.
PYTHONIOENCODING
If this is set before running the interpreter, it overrides the encoding used for
stdin/stdout/stderr, in the syntax encodingname:errorhandler The errorhandler part is optional and
has the same meaning as in str.encode. For stderr, the errorhandler
part is ignored; the handler will always be ´backslashreplace´.
PYTHONNOUSERSITE
If this is set to a non-empty string it is equivalent to specifying the -s option (Don't add the
user site directory to sys.path).
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.
PYTHONWARNINGS
If this is set to a comma-separated string it is equivalent to specifying the -W option for each
separate value.
PYTHONHASHSEED
If this variable is set to "random", a random value is used to seed the hashes of str and bytes
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
disable hash randomization.
PYTHONMALLOC
Set the Python memory allocators and/or install debug hooks. The available memory allocators are
malloc and pymalloc. The available debug hooks are debug, malloc_debug, and pymalloc_debug.
When Python is compiled in debug mode, the default is pymalloc_debug and the debug hooks are
automatically used. Otherwise, the default is pymalloc.
PYTHONMALLOCSTATS
If set to a non-empty string, Python will print statistics of the pymalloc memory allocator every
time a new pymalloc object arena is created, and on shutdown.
This variable is ignored if the $PYTHONMALLOC environment variable is used to force the malloc(3)
allocator of the C library, or if Python is configured without pymalloc support.
PYTHONASYNCIODEBUG
If this environment variable is set to a non-empty string, enable the debug mode of the asyncio
module.
PYTHONTRACEMALLOC
If this environment variable is set to a non-empty string, start tracing Python memory allocations
using the tracemalloc module.
The value of the variable is the maximum number of frames stored in a traceback of a trace. For
example, PYTHONTRACEMALLOC=1 stores only the most recent frame.
PYTHONFAULTHANDLER
If this environment variable is set to a non-empty string, faulthandler.enable() is called at
startup: install a handler for SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals to dump the
Python traceback.
This is equivalent to the -X faulthandler option.
PYTHONEXECUTABLE
If this environment variable is set, sys.argv[0] will be set to its value instead of the value got
through the C runtime. Only works on Mac OS X.
PYTHONUSERBASE
Defines the user base directory, which is used to compute the path of the user site-packages
directory and Distutils installation paths for python setup.py install --user.
PYTHONPROFILEIMPORTTIME
If this environment variable is set to a non-empty string, Python will show how long each import
takes. This is exactly equivalent to setting -X importtime on the command line.
PYTHONBREAKPOINT
If this environment variable is set to 0, it disables the default debugger. It can be set to the
callable of your debugger of choice.
Debug-mode variables
Setting these variables only has an effect in a debug build of Python, that is, if Python was configured
with the --with-pydebug build option.
PYTHONTHREADDEBUG
If this environment variable is set, Python will print threading debug info.
PYTHONDUMPREFS
If this environment variable is set, Python will dump objects and reference counts still alive
after shutting down the interpreter.
AUTHOR
The Python Software Foundation: https://www.python.org/psf/
INTERNET RESOURCES
Main website: https://www.python.org/
Documentation: https://docs.python.org/
Developer resources: https://devguide.python.org/
Downloads: https://www.python.org/downloads/
Module repository: https://pypi.org/
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 otherwise using Python and for a
DISCLAIMER OF ALL WARRANTIES.
PYTHON(1)