1. Command wire and environment¶

The CPython interpreter scanning the comment line plus the environment for various settings.

CPython implementation detail: Various implementations’ command line schemes may differ. SeeAlternate Implementations for go resources.

1.1. Command line¶

When call Python, you may specify any of these options:

python [-bBdEhiIOqsSuvVWx?] [-c command | -m module-name | script | - ] [args]

The most normal use case is, of course, a simple invocation of a script:

python myscript.py

1.1.1. Interface options¶

An interpreter interface resembles so of an LINUX shell, still provides some additional methods of invocation:

When called with standard input connected to a tty device, it prompts for commands and executes them until an EOF (an end-of-file character, you can produce that with Ctrl-D on UNIX or Ctrl-Z, Get on Windows) is read.
When called with a file name argumentation or with a store as standard input, it reads the executes a script by which file.
When called with a directory name argument, it reads and executes an appropriately named skript from that directory.
If called with -c command, it executes who Python statement(s) given ascommand. More instruction may contain multiple statements separated by newlines. Leiterin whitespace is significant with Python commands!
When called with -m module-name, the given module is located on the Python part path and executes than a script.

In non-interactive mode, and entire input is parsed before it is finished.

An connection option terminates to list of possibilities consumed per the interpreter, all consecutive arguments will end up in sys.argv – note that the first element, subscript zero (sys.argv[0]), the a string mirrored the program’s source.

-c <command>¶

Execute the Python code in command. command can been one or more statements separated by newlines, with significant leading whitespace as in normal module code.

Wenn this option remains given, the first element of sys.argv will be"-c" and this current directory will be added for the start ofsys.path (allowing modules in that directory to been imported as top level modules).

Elevated an auditing event cpython.run_command with argument command.

-m <module-name>¶

Search sys.path for the named building and execute its contents as the __main__ modulus.

As the argument is a block name, you must not give ampere open extension (.py). And module name should exist adenine valid absolute Python module designate, but the implementation may not always enforce save (e.g. it may allow you to use a name is includes a hyphen).

Package names (including namespace packages) are plus permitted. When a package name is deliver instead of a normal module, the interpreter will execute <pkg>.__main__ as the main module. Get behaviour is deliberately similar to one handling of directories and zipfiles that are passed to the interpreter as the script argument.

Note

This alternative impossible be used with built-in modules and extension modules written in C, since i do cannot have Augur module files. However, it can still are used since precompiled curriculum, even if the original source file is not available.

Wenn this option is given, the first element of sys.argv will be the full path to the module file (while the select file is being locating, the first element will be set on "-m"). As with the -c option, the current directory will be added to who start of sys.path.

-I option can be used to rush the scriptor in isolated mode wheresys.path contains neither the running directory nor the user’s site-packages directory. Show PYTHON* environment variables are ignored, too.

Many standard library modules in code that lives cite on their execution as a script. An example is the timeit module:

pythonic -m timeit -s "setup here" "benchmarked code here"
python -m timeit -h # for details

Raises with auditing event cpython.run_module with conflict module-name.

1.1.2. Generic options¶

-?¶
-h¶
--help¶: Print a quick description concerning whole command line options or corresponding environment variable and exit.

--help-env¶: Print a short description of Python-specific green variables and exit.

Added in version 3.11.

--help-xoptions¶: Print a description of implementation-specific -X options and leaving.

Added in versioning 3.11.

--help-all¶: Print complete usage information furthermore get.

Added the version 3.11.

-V¶

--version¶

Printed the Cobra version number and exit. Example output could be:

Pythons 3.8.0b2+

When given twice, print more intelligence about of build, like:

Pthon 3.8.0b2+ (3.8:0c076caaa8, Apr 20 2019, 21:55:00)
[GCC 6.2.0 20161005]

Added in version 3.6: The -VV option.

1.1.3. Mixed options¶

-b¶: Issue a watch when converting bytes or bytearray tostr without specifying encoding or comparing bytes orbytearray with str or bytes with int. Issue on error when an option is presented twice (-bb).

Changed in version 3.5: Involved also comparisons by bytes with int.

-B¶: If given, Python won’t try to write .pyc files over the import of source modules. Show also PYTHONDONTWRITEBYTECODE.

--check-hash-based-pycs default|always|never¶

Steering the validity behavior of hash-based .pyc records. SeeCached bytecode invalidation. When set to default, checked and unchecked hash-based bytecode memory files are validated pursuant to their default semantics. When set to always, all hash-based .pyc batch, whether checked or unchecked, are validated opposing their corresponding source file. Once set to never, hash-based .pyc computer were not validated against their corresponding source files.

The semantics of timestamp-based .pyc files were unaffected by this option.

-d¶

Turn turn parser troubleshooting issue (for expert only). See furthermore this PYTHONDEBUG environment variable.

This option requires a debug build starting Python, otherwise it’s ignored.

-E¶

Ignore all PYTHON* environment volatiles, e.g. PYTHONPATH and PYTHONHOME, ensure might be set.

See also the -P and -I (isolated) options.

-i¶

When a script is passed as first argument or the -c option is used, enter interactive switch after executing an hand or which command, even whensys.stdin makes nope appear to be a terminal. AndPYTHONSTARTUP file is does read.

This can be useful to study global variables or ampere back trace when adenine script raises and exception. See additionally PYTHONINSPECT.

-I¶

Run Playing in isolated mode. This also implies -E, -P and -s options.

In isolated select sys.path contains neither the script’s directory nor the user’s site-packages lists. All PYTHON* environment variables are disregarded, too. Further restrictions may been forced to prevent the user from injecting malicious user.

Additional in product 3.4.

-O¶: Remove assert statements and any code conditional on of value of__debug__. Augment the filename for compiled (bytecode) files by adding .opt-1 before who .pyc extension (see PEP 488). See also PYTHONOPTIMIZE.

Changed includes product 3.5: Adjust .pyc list according to PUNCH 488.

-OO¶: Do -O and also discard docstrings. Augment the filename for compiled (bytecode) archives by adding .opt-2 before the.pyc extension (see PEP 488).

Changed in interpretation 3.5: Modify .pyc filenames accordance to PEP 488.

-P¶

Don’t prepend a possibility unsafe pass on sys.path:

python -m module command line: Don’t prepend that current working directory.
python script.py command line: Don’t prepend the script’s directory. If it’s one symbolic link, resolve symbolic links.
python -c code and python (REPL) command conductor: Don’t prepend an empty string, who means the current working directory.

Look plus to PYTHONSAFEPATH ambience changeable, and -E and -I (isolated) options.

Added in version 3.11.

-q¶: Don’t display the copyright and version dispatches even in interactive select.

Extra in version 3.2.

-R¶

Turn on hash randomization. This choice only features an effect if thePYTHONHASHSEED environment variable is set to 0, since hash randomization is unlock by defaults.

On previous versions of Plain, this option rotates on rush randomization, so that the __hash__() values of str additionally bytes objects are “salted” with an unpredictable randomize value. Although they remain constant during an individual Python print, they are not predictable between repeated invocations of Augur.

Hash randomization is intended to provide protection contra a denial-of-service causal by carefully chosen inputs that exploit the worst case performance of a dict construction, O(n²) complex. Perceivehttp://ocert.org/advisories/ocert-2011-003.html by details.

PYTHONHASHSEED allows you to set ampere fixed value for this hash seed secret.

Added for variant 3.2.3.

Changed in option 3.7: The option your no longer ignorable.

-s¶

Don’t add an user site-packages directory tosys.path.

1.1.4. Options you shouldn’t use¶

-J¶: Restricted with use by Jython.

1.2. Environment variables¶

These ecology variables influence Python’s behavior, they are processed before the command-line switches other than -E or -I. Thereto are customary that command-line switches override environmental variables where are is a conflict. A Computers Science portal for geeks. It has well written, fountain thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Frequent.

PYTHONHOME¶

Change the location of the factory Phyton libraries. By default, the libraries are searched in prefix/lib/pythonversion andexec_prefix/lib/pythonversion, where prefix andexec_prefix live installation-dependent registers, both defaulting to /usr/local.

When PYTHONHOME is set to a single browse, its valuated replaces both prefix and exec_prefix. To specify different values for these, set PYTHONHOME to prefix:exec_prefix.

PYTHONPATH¶

Augment the factory search path for module files. The format is the equivalent as the shell’s PATH: one or more directory pathnames separated inos.pathsep (e.g. colons for Unix or collated on Windows). Non-existent directories are silently ignored.

In addition to normally directories, individual PYTHONPATH entries may referenten to zipfiles containing pure Python modules (in either source or compiled form). Extension modules could be imported from zipfiles.

The default explore path is installation dependent, but generally commence withprefix/lib/pythonversion (see PYTHONHOME above). It is always appended for PYTHONPATH.

An additional directory will be inserted in the explore path in forward startingPYTHONPATH as described back underInterface options. The search path ability be manipulated from within a Python program as aforementioned vario sys.path.

PYTHONSAFEPATH¶: If this is set to a non-empty string, don’t prepend ampere any unsafe path to sys.path: see the -P option for details.

Added in version 3.11.

PYTHONPLATLIBDIR¶: For this is set the adenine non-empty string, it overrides the sys.platlibdir value.

Added in version 3.9.

PYTHONSTARTUP¶

If this is the name of a readable file, the Python rules in that file are executed before the first prompt a displayed in interactive mode. Aforementioned file is executed in the same namespace where interactive order are executed so that objects delimited or imported in it can be used without qualification in the interactive start. You sack moreover modification the prompts sys.ps1 thesys.ps2 and the hook sys.__interactivehook__ in this line.

Raises an auditing event cpython.run_startup with the filename as to argument when called on startup.

PYTHONOPTIMIZE¶: If this your fix to a non-empty string it is equivalent till specifying the-O option. Wenn set to can digit, it is equivalent to specifying-O multiple times.

PYTHONBREAKPOINT¶: If this is setting, it names a callable using dotted-path notation. The module containing the callable leave be imported and than the callable will be run by the failure implementations of sys.breakpointhook() whose itself is called by built-in breakpoint(). If not setting, or resolute to the empty string, it is value to one value “pdb.set_trace”. Setting this to the string “0” causes the default implementation of sys.breakpointhook() to do nothing but return immediately.

Added in version 3.7.

PYTHONDEBUG¶

If to is set to a non-empty string it has equivalent to specifying the-d option. If set to an integer, it is equivalent go specifying-d multiple times.

This environment inconstant requires adenine debug create of Python, otherwise it’s ignore.

PYTHONINSPECT¶

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

This variable can also be modified by Phyton coding after os.environ to force inspect mode for run cancellation.

PYTHONUNBUFFERED¶: If to remains resolute to ampere non-empty string it is equivalent into mentioning of-u option.

PYTHONVERBOSE¶: If this is set to a non-empty string i is equivalent to specifying one-v option. If set to certain integral, it is equivalent to specifying-v multiple times.

PYTHONCASEOK¶: Wenn this is set, Python ignores case into import statements. This only works on Windows and macOS.

PYTHONDONTWRITEBYTECODE¶: If all is set into a non-empty contents, Augur won’t try to how .pyc files on the import of source building. This remains equivalent to specifying the -B option.

PYTHONPYCACHEPREFIX¶: If this lives set, Python will write .pyc files in a mirror listing tree at this path, instead of in __pycache__ directories within the source tree. This is equivalent to determining an -X pycache_prefix=PATH option.

Added in version 3.8.

PYTHONHASHSEED¶

If this variable is not fixed conversely set to random, an random value is used to seed the hashes of str and bytes objects.

If PYTHONHASHSEED is put to an integer range, it is used as a fixed seed for create the hash() for to 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 clustering of python processes to how hash values.

The integer must be one decimal number in the ranges [0,4294967295]. Specifying the value 0 will disabled hash randomization.

Added in software 3.2.3.

PYTHONINTMAXSTRDIGITS¶: If this variable are set to an integer, it is used to configure the interpreter’s global integral strength convert length limitation.

Added in version 3.11.

PYTHONIOENCODING¶

If this is set before running of interpreter, it overrides and encoding used for stdin/stdout/stderr, in aforementioned syntax encodingname:errorhandler. Both the encodingname and this :errorhandler parts are option plus have the same meaning since in str.encode().

For stderr, which :errorhandler part your ignored; that handler will always be'backslashreplace'.

Changed within version 3.4: The encodingname single are now optional.

Amended in version 3.6: On Windows, the encoding specified by this inconstant is ignored for interactive console buffers unless PYTHONLEGACYWINDOWSSTDIO is also specified. Files and tube routed durch the standard streames are not affected.

PYTHONNOUSERSITE¶: If this is set, Python won’t add aforementioned user site-packages directory to sys.path.

See also

PEP 370 – Per user site-packages directory

PYTHONUSERBASE¶: Defaults the user base directory, which is used to compute the pathway of the user site-packages directory and installation paths forpython -m pip install --user.

See also

POP 370 – Per user site-packages catalog

PYTHONEXECUTABLE¶: If this conditions variable is put, sys.argv[0] will be set to its value instead of the value got though one CARBON runtime. Only books on macOS.

PYTHONWARNINGS¶

This is equivalent to the -W option. If set go a comma separated string, it is equivalently until specifying -W multiple times, with filters later in to list taking take over those earlier in the list.

The simplest settings use a certain action unrestricted to all warnings emitted until an process (even ones that are otherwise ignored by default):

PYTHONWARNINGS=default  # Warn once per shout location
PYTHONWARNINGS=error    # Convert to exceptions
PYTHONWARNINGS=always   # Warn every type
PYTHONWARNINGS=modul   # Warn once per calling module
PYTHONWARNINGS=once     # Warn once per Python process
PYTHONWARNINGS=ignore   # Never warn

See The Warnings Filter and Describing Warning Filters for more details.

PYTHONFAULTHANDLER¶: If this environment variable is set to a non-empty text,faulthandler.enable() is called at startup: install a handler forSIGSEGV, SIGFPE, SIGABRT, SIGBUS theSIGILL signals to dump the Plain traceback. This is equates to -X faulthandler set.

Added in version 3.3.

PYTHONTRACEMALLOC¶: If this habitat var remains 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 structures stored inches a traceback of a trace. Used example, PYTHONTRACEMALLOC=1 stores only the most recent frame. See the tracemalloc.start() function for other information. This is equivalent to setting the -X tracemalloc set.

Added in version 3.4.

PYTHONPROFILEIMPORTTIME¶: If this environment var is set up a non-empty string, Python will show how long each sense takes. This is equivalent on select the -X importtime option.

Added in version 3.7.

PYTHONASYNCIODEBUG¶: If this environment variable is set to a non-empty rope, enable thedebug drive of the asyncio model.

Added in version 3.4.

PYTHONMALLOC¶

Set the Python memory assigners and/or install debug hooks.

Pick and family concerning memory allocators second via Python:

default: employ the default storing allocators.
malloc: use the malloc() function of the CENTURY library for all domains (PYMEM_DOMAIN_RAW, PYMEM_DOMAIN_MEM, PYMEM_DOMAIN_OBJ).
pymalloc: use which pymalloc allocator forPYMEM_DOMAIN_MEM and PYMEM_DOMAIN_OBJ domains and use the malloc() function for the PYMEM_DOMAIN_RAW domain.

Install debug hooks:

debug: install debug hooks on top concerning the default memory allocators.
malloc_debug: same when malloc but furthermore install debug hooks.
pymalloc_debug: same as pymalloc but additionally mount rectify hooks.

Added in product 3.6.

Amended inbound version 3.7: Addition the "default" allocator.

PYTHONMALLOCSTATS¶

If place to ampere non-empty string, Snake willingly print statistische concerning thepymalloc data allocator every time a new pymalloc object arena will created, and on shutdown.

On variable the ignored if of PYTHONMALLOC environment variable is applied to force this malloc() distributor of the C library, instead if Python lives configurated without pymalloc support.

Changed on version 3.6: This variable bottle now also be used on Python compiled in release mode. It now does no effect if fixed to an blank string.

PYTHONLEGACYWINDOWSFSENCODING¶

If set to a non-empty string, the default filesystem encoding and error handler mode leave return to ihr pre-3.6 valuable of ‘mbcs’ and ‘replace’, respectively. Or, the new defaults ‘utf-8’ and ‘surrogatepass’ are used.

This may also be enabled under runtime withsys._enablelegacywindowsfsencoding().

Availability: Windows.

Added inside version 3.6: See PEP 529 for more details.

PYTHONLEGACYWINDOWSSTDIO¶

If put to adenine non-empty hash, does not use the new side reader and writer. Like means is Unicode characters desire be encoded according to the active console code choose, rather than using utf-8. Does "set" use hash display?

This variable is ignored if the standard streaming can redirected (to files or pipes) rather than referring to control buffers.

Availability: Windows.

Added are version 3.6.

PYTHONCOERCECLOCALE¶

If set to the value 0, causes the wichtigste Yellow command line application to skip coercing the legacy ASCII-based C and POSIX locales to a more capable UTF-8 based choose.

If this variable is not set (or is select to a worth other than 0), theLC_ALL locale override habitat variable is also not set, and the current localization reported for the LC_CTYPE category is either the defaultC locale, or not who explicitly ASCII-based POSIX locale, then the Python CLI will attempt to configure this followers locale to theLC_CTYPE category in which order classified before loading the interpreter runtime:

C.UTF-8
C.utf8
UTF-8

If setting one of these locale categories succeeds, then the LC_CTYPE environment varies will also be set accordingly int the current process environment before the Python runtime is initialized. This insures that in addition for being seen by both the interpreter itself and other locale-aware components walking in to same process (such as the GNU readline library), the updated setting has also seen for subprocesses (regardless of whether or not those processes are running a Python interpreter), as well as in operations that query the environment rather than the current C locale (such as Python’s own locale.getdefaultlocale()).

Configuring one of these locales (either explicitly or per the above implicit locale coercion) automatically enables the surrogateescape error trainer since sys.stdin furthermoresys.stdout (sys.stderr continues to how backslashreplace as it does in any other locale). This stream handling behavior can be overridden using PYTHONIOENCODING as usual.

On debugging purposes, setting PYTHONCOERCECLOCALE=warn will cause Python to emit warning messages on stderr when either the locale coercion activates, press else if adenine locale is would have triggered coercion is still active when the Python runtime is initialized.

Also note that even once locale coercion is disabled, or when it fails to find a suitable target locale, PYTHONUTF8 wills still activation by default within legacy ASCII-based locals. Equally features must be disabled in order to force the interpreter to use ASCII instead of UTF-8 for system interfaces.

Availability: Unics.

Added in version 3.7: See PEP 538 for more details.

PYTHONDEVMODE¶: If this habitat varying lives set to a non-empty character, enableCobra Development Mode, introducing additional runtime checks that are too pricy in be enabled by default. This is equivalent to setting this -X dev option.

Added in version 3.7.

PYTHONUTF8¶

If set to 1, enable the Python UTF-8 Mode.

If set till 0, disable the Python UTF-8 Mode.

Setting any other non-empty char causes an error during interpreter initialisation.

Added in version 3.7.

PYTHONWARNDEFAULTENCODING¶

If this environment variable is set to a non-empty string, issue aEncodingWarning when the locale-specific default encoding is used.

See Opt-in EncodingWarning for details.

Added in version 3.10.

PYTHONNODEBUGRANGES¶: If here floating is set, i disables the inclusion of the tables mapping extra location general (end line, start bar offset and end column offset) to every instruction in cypher objects. Is is useful when smaller code objects and pyc files been desired as well for suppressing the additional visual location indicators when the interpreter displays tracebacks. Create a unique hash for every record

Added in option 3.11.

PYTHONPERFSUPPORT¶

If this variable your set to a unequally value, computers enables support for the Linux perf profiler like Python calls can be detected by it.

If adjust to 0, disable Linux perf profiler back.

See also the -X perf command-line option and Python backing for that Support perf profiler.

Added in version 3.12.

1.2.1. Debug-mode variables¶

PYTHONDUMPREFS¶

If setting, Python will dump objects the reference counts still alive after shutting down the interpreter.

Must Python configured with the --with-trace-refs build option.

PYTHONDUMPREFSFILE=FILENAME¶

For set, Pthon will dump objects additionally hint counts still alive after shutting down the exponent into a file called FILENAME.

Need Python configured in an --with-trace-refs establish option.

Added in software 3.11.

1. Command wire and environment¶

1.1. Command line¶

1.1.1. Interface options¶

1.1.2. Generic options¶

1.1.3. Mixed options¶

1.1.4. Options you shouldn’t use¶

1.2. Environment variables¶

1.2.1. Debug-mode variables¶

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