Простое руководство по аргументам командной строки Python
Одна из сильнейших сторон Python — способность выполнять любые задачи. Его стандартная библиотека предоставляет достаточно функций для написания множества полезных сценариев и инструментов. А для получения больших возможностей можно просто воспользоваться pip install .
Почти каждый современный ЯП способен принимать аргументы из командной строки. Это очень важная функция, поскольку она допускает динамический ввод данных от пользователей, независимо от того, написали они программу или нет.
Python содержит несколько библиотек, благодаря которым код может принимать введенные пользователем данные из команды, таких как sys.argv , getopt и argparse . На данный момент argparse — наилучший и наиболее распространенный вариант.
Библиотека Python argparse была выпущена как часть стандартной библиотеки вместе с Python 3.2. После этого релиза в силу своей популярности она была интегрирована в Python 2.7 и во все будущие версии Python, быстро став золотым стандартом для работы с аргументами командной строки. Она предоставляет следующие функции:
- Возможность настройки справочных сообщений и документации для аргументов командной строки.
- Установка значений по умолчанию для аргументов в чистом и читабельном виде.
- Наличие заданного количества опций для определенного аргумента командной строки.
- Поддержка переменного количества параметров для одного аргумента.
- Возможность автоматически применять действие или функцию к вводу по определенным указаниям.
Проведем небольшую экскурсию по библиотеке argparse Python.
Начальная установка
Откройте пустой сценарий Python. Библиотека argparse встроена в Python, соответственно процедура установки не потребуется. На фрагменте кода ниже показано, как создать начальную установку для argparse:
В этом коде есть 3 важных компонента:
- Импорт argparse .
- Создание парсера аргументов (с описанием).
- Парсинг аргументов командной строки.
На втором этапе мы создаем объект parser, с помощью которого можно добавлять аргументы командной строки вместе с опциями для каждого из них. На третьем этапе запускается функция, которая извлекает введенные пользователем аргументы из командной строки.
Прелесть argparse заключается в том, что она автоматически работает с командной строкой с помощью этой простой настройки. Запустите программу с —help в конце и argparse выведет описание руководства по argparse!
Теперь добавим аргумент командной строки с именем “a”, как показано во фрагменте кода ниже. Чтобы передать аргумент командной строки в сценарий Python, запустите его с помощью python3 argparse_2.py —a=5 :
Обратите внимание на использование функции .add_argument() для передачи "a" в качестве аргумента командной строки. Чтобы получить доступ к переменной, полученной из a , используем args.a .
Следует отметить, что без указания значения для a в командной строке args.a будет None . Чтобы обойти это, указываем значение по умолчанию для a в парсере аргумента, как показано ниже. Обратите внимание, что на этот раз также добавлено описание.
В данном случае, если мы не передадим значение для a через командную строку, то a приобретет значение по умолчанию, равное 1. Добавив строку для переменной help , мы также сможем напечатать более эффективное описание для каждой переменной, используя —help :
Простые варианты использования аргументов командной строки
Рассмотрим еще несколько интересных опций с argparse . Во-первых, мы можем указать информацию о типе каждой переменной так, чтобы преобразование типов выполнялось прямо на входе:
Чтобы убедиться, что пользователь всегда передает значение для определенного аргумента можно использовать ключевое слово required . Установленное значение True вынуждает пользователя вводить данные только для этого значения, иначе программа выдаст ошибку и остановится.
Если мы установим значение для аргумента —name , то программа будет работать отлично! Однако при его отсутствии мы получим подобное сообщение об ошибке:
Мы также можем ввести возможные значения для определенного аргумента командной строки с помощью аргумента choices . Полезная функция, особенно при наличии в коде набора операторов if-else, которые выполняют определенные операции на основе одной строки. Пример:
Теперь при вводе любого значения, находящегося в списке choices, код будет работать и примет аргумент education . Однако при вводе того, что отсутствует в списке, например, числа 5 , вы получите следующее сообщение, в котором предлагается выбрать варианты из списка:
Продвинутые варианты использования и советы
Настало время двигаться дальше и перейти к продвинутому argparse!
В аргументе action можно указать действие, которое должен принимать парсер аргументов. Например, аргумент, который автоматически устанавливается равным булевому значению True , если оно присутствует или является константой. В примере ниже показаны оба случая.
В приведенном выше коде говорится, что если в командной строке присутствует аргумент a , то он будет иметь значение True , а в противном случае False . Аналогичным образом, при наличии аргумента командной строки b он должен иметь значение 10 , а в противном случае None из-за отсутствия значения по умолчанию!
Мы также можем установить так называемые взаимоисключающие группы, определяющие набор аргументов командной строки парсера, которые не могут быть переданы одновременно.
Аргументы argparse — a и b — добавлены в одну взаимоисключающую группу. Таким образом, Python не позволит отправлять a и b одновременно, подобно python3 argparse_8.py —a —b . Эта функция гарантирует, что пользователь не передаст противоречащие друг другу переменные одновременно, что позволяет избежать путаницы или ошибок.
Вот и все! Вы прошли простое руководство по аргументам командной строки Python.
1. Command line and environment¶
The CPython interpreter scans the command line and the environment for various settings.
CPython implementation detail: Other implementations’ command line schemes may differ. See Alternate Implementations for further resources.
1.1. Command line¶
When invoking Python, you may specify any of these options:
The most common use case is, of course, a simple invocation of a script:
1.1.1. Interface options¶
The interpreter interface resembles that of the UNIX shell, but 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, Enter on Windows) 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 a directory name argument, it reads and executes an appropriately named script from that directory.
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!
When called with -m module-name , the given module is located on the Python module path and executed as a script.
In non-interactive mode, the entire input is parsed before it is executed.
An interface option terminates the list of options consumed by the interpreter, all consecutive arguments will end up in sys.argv – note that the first element, subscript zero ( sys.argv[0] ), is a string reflecting the program’s source.
Execute the Python code in command. command can be one or more statements separated by newlines, with significant leading whitespace as in normal module code.
If this option is given, the first element of sys.argv will be "-c" and the current directory will be added to the start of sys.path (allowing modules in that directory to be imported as top level modules).
Raises an auditing event cpython.run_command with argument command .
Search sys.path for the named module and execute its contents as the __main__ module.
Since the argument is a module name, you must not give a file extension ( .py ). The module name should be a valid absolute Python module name, but the implementation may not always enforce this (e.g. it may allow you to use a name that includes a hyphen).
Package names (including namespace packages) are also permitted. When a package name is supplied instead of a normal module, the interpreter will execute <pkg>.__main__ as the main module. This behaviour is deliberately similar to the handling of directories and zipfiles that are passed to the interpreter as the script argument.
This option cannot be used with built-in modules and extension modules written in C, since they do not have Python module files. However, it can still be used for precompiled modules, even if the original source file is not available.
If this option is given, the first element of sys.argv will be the full path to the module file (while the module file is being located, the first element will be set to "-m" ). As with the -c option, the current directory will be added to the start of sys.path .
-I option can be used to run the script in isolated mode where sys.path contains neither the current directory nor the user’s site-packages directory. All PYTHON* environment variables are ignored, too.
Many standard library modules contain code that is invoked on their execution as a script. An example is the timeit module:
Raises an auditing event cpython.run_module with argument module-name .
Equivalent functionality directly available to Python code
PEP 338 – Executing modules as scripts
Changed in version 3.1: Supply the package name to run a __main__ submodule.
Changed in version 3.4: namespace packages are also supported
Read commands from standard input ( sys.stdin ). If standard input is a terminal, -i is implied.
If this option is given, the first element of sys.argv will be "-" and the current directory will be added to the start of sys.path .
Raises an auditing event cpython.run_stdin with no arguments.
Execute the Python code contained in script, which must be a filesystem path (absolute or relative) referring to either a Python file, a directory containing a __main__.py file, or a zipfile containing a __main__.py file.
If this option is given, the first element of sys.argv will be the script name as given on the command line.
If the script name refers directly to a Python file, the directory containing that file is added to the start of sys.path , and the file is executed as the __main__ module.
If the script name refers to a directory or zipfile, the script name is added to the start of sys.path and the __main__.py file in that location is executed as the __main__ module.
-I option can be used to run the script in isolated mode where sys.path contains neither the script’s directory nor the user’s site-packages directory. All PYTHON* environment variables are ignored, too.
Raises an auditing event cpython.run_file with argument filename .
Equivalent functionality directly available to Python code
If no interface option is given, -i is implied, sys.argv[0] is an empty string ( "" ) and the current directory will be added to the start of sys.path . Also, tab-completion and history editing is automatically enabled, if available on your platform (see Readline configuration ).
Changed in version 3.4: Automatic enabling of tab-completion and history editing.
1.1.2. Generic options¶
Print a short description of all command line options and corresponding environment variables and exit.
Print a short description of Python-specific environment variables and exit.
New in version 3.11.
Print a description of implementation-specific -X options and exit.
New in version 3.11.
Print complete usage information and exit.
New in version 3.11.
Print the Python version number and exit. Example output could be:
When given twice, print more information about the build, like:
New in version 3.6: The -VV option.
1.1.3. Miscellaneous options¶
Issue a warning when comparing bytes or bytearray with str or bytes with int . Issue an error when the option is given twice ( -bb ).
Changed in version 3.5: Affects comparisons of bytes with int .
If given, Python won’t try to write .pyc files on the import of source modules. See also PYTHONDONTWRITEBYTECODE .
Control the validation behavior of hash-based .pyc files. See Cached bytecode invalidation . When set to default , checked and unchecked hash-based bytecode cache files are validated according to their default semantics. When set to always , all hash-based .pyc files, whether checked or unchecked, are validated against their corresponding source file. When set to never , hash-based .pyc files are not validated against their corresponding source files.
The semantics of timestamp-based .pyc files are unaffected by this option.
Turn on parser debugging output (for expert only, depending on compilation options). See also PYTHONDEBUG .
Ignore all PYTHON* environment variables, e.g. PYTHONPATH and PYTHONHOME , that might be set.
See also the -P and -I (isolated) 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, even when sys.stdin does not appear to be a terminal. The PYTHONSTARTUP file is not read.
This can be useful to inspect global variables or a stack trace when a script raises an exception. See also PYTHONINSPECT .
Run Python in isolated mode. This also implies -E , -P and -s options.
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.
New in version 3.4.
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 (see PEP 488). See also PYTHONOPTIMIZE .
Changed in version 3.5: Modify .pyc filenames according to PEP 488.
Do -O and also discard docstrings. Augment the filename for compiled ( bytecode ) files by adding .opt-2 before the .pyc extension (see PEP 488).
Changed in version 3.5: Modify .pyc filenames according to PEP 488.
Don’t prepend a potentially unsafe path to sys.path :
python -m module command line: Don’t prepend the current working directory.
python script.py command line: Don’t prepend the script’s directory. If it’s a symbolic link, resolve symbolic links.
python -c code and python (REPL) command lines: Don’t prepend an empty string, which means the current working directory.
See also the PYTHONSAFEPATH environment variable, and -E and -I (isolated) options.
New in version 3.11.
Don’t display the copyright and version messages even in interactive mode.
New in version 3.2.
Turn on hash randomization. This option only has an effect if the PYTHONHASHSEED environment variable is set to 0 , since hash randomization is enabled by default.
On previous versions of Python, this option turns on hash randomization, so that the __hash__() values of str and bytes objects are “salted” with an unpredictable random value. Although they remain constant within an individual Python process, they are not predictable between repeated invocations of Python.
Hash randomization 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.
PYTHONHASHSEED allows you to set a fixed value for the hash seed secret.
Changed in version 3.7: The option is no longer ignored.
New in version 3.2.3.
PEP 370 – Per user site-packages directory
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 (call site.main() if you want them to be triggered).
Force the stdout and stderr streams to be unbuffered. This option has no effect on the stdin stream.
Changed in version 3.7: The text layer of the stdout and stderr streams now is 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 ( -vv ), print a message for each file that is checked for when searching for a module. Also provides information on module cleanup at exit.
Changed in version 3.10: The site module reports the site-specific paths and .pth files being processed.
Warning control. Python’s warning machinery by default prints warning messages to sys.stderr .
The simplest settings apply a particular action unconditionally to all warnings emitted by a process (even those that are otherwise ignored by default):
The action names can be abbreviated as desired and the interpreter will resolve them to the appropriate action name. For example, -Wi is the same as -Wignore .
The full form of argument is:
Empty fields match all values; trailing empty fields may be omitted. For example -W ignore::DeprecationWarning ignores all DeprecationWarning warnings.
The action field is as explained above but only applies to warnings that match the remaining fields.
The message field must match the whole warning message; this match is case-insensitive.
The category field matches the warning category (ex: DeprecationWarning ). 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 module field matches the (fully qualified) module name; this match is case-sensitive.
The lineno field matches the line number, where zero matches all line numbers and is thus equivalent to an omitted line number.
Multiple -W options can be given; when a warning matches more than one option, the action for the last matching option is performed. Invalid -W options are ignored (though, a warning message is printed about invalid options when the first warning is issued).
Warnings can also be controlled using the PYTHONWARNINGS environment variable and from within a Python program using the warnings module. For example, the warnings.filterwarnings() function can be used to use a regular expression on the warning message.
Skip the first line of the source, allowing use of non-Unix forms of #!cmd . This is intended for a DOS specific hack only.
Reserved for various implementation-specific options. CPython currently defines the following possible values:
-X faulthandler to enable faulthandler ;
-X showrefcount to 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 to 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. See the tracemalloc.start() for more information.
-X importtime to 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’ . See also PYTHONPROFILEIMPORTTIME .
-X dev : enable Python Development Mode , introducing additional runtime checks that are too expensive to be enabled by default.
-X utf8 enables the Python UTF-8 Mode . -X utf8=0 explicitly disables Python UTF-8 Mode (even when it would otherwise activate automatically).
-X pycache_prefix=PATH enables writing .pyc files to a parallel tree rooted at the given directory instead of to the code tree. See also PYTHONPYCACHEPREFIX .
-X warn_default_encoding issues a EncodingWarning when the locale-specific default encoding is used for opening files. See also PYTHONWARNDEFAULTENCODING .
-X no_debug_ranges disables the inclusion of the tables mapping extra location information (end line, start column offset and end column offset) to every instruction in code objects. This is useful when smaller code objects and pyc files are desired as well as suppressing the extra visual location indicators when the interpreter displays tracebacks. See also PYTHONNODEBUGRANGES .
-X frozen_modules determines whether or not frozen modules are ignored by the import machinery. A value of “on” means they get imported and “off” means they are ignored. The default is “on” if this is an installed Python (the normal case). If it’s under development (running from the source tree) then the default is “off”. Note that the “importlib_bootstrap” and “importlib_bootstrap_external” frozen modules are always used, even if this flag is set to “off”.
It also allows passing arbitrary values and retrieving them through the sys._xoptions dictionary.
Changed in version 3.2: The -X option was added.
New in version 3.3: The -X faulthandler option.
New in version 3.4: The -X showrefcount and -X tracemalloc options.
New in version 3.6: The -X showalloccount option.
New in version 3.7: The -X importtime , -X dev and -X utf8 options.
New in version 3.8: The -X pycache_prefix option. The -X dev option now logs close() exceptions in io.IOBase destructor.
Changed in version 3.9: Using -X dev option, check encoding and errors arguments on string encoding and decoding operations.
The -X showalloccount option has been removed.
New in version 3.10: The -X warn_default_encoding option.
Deprecated since version 3.9, removed in version 3.10: The -X oldparser option.
New in version 3.11: The -X no_debug_ranges option.
New in version 3.11: The -X frozen_modules option.
New in version 3.11: The -X int_max_str_digits option.
1.1.4. Options you shouldn’t use¶
Reserved for use by Jython.
1.2. Environment variables¶
These environment variables influence Python’s behavior, they are processed before the command-line switches other than -E or -I. It is customary that command-line switches override environmental variables where there is a conflict.
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 .
Augment the default search path for module files. The format is the same as the shell’s PATH : one or more directory pathnames separated by os.pathsep (e.g. colons on Unix or semicolons on Windows). Non-existent directories are silently ignored.
In addition to normal directories, individual PYTHONPATH entries may refer to zipfiles containing pure Python modules (in either source or compiled form). Extension modules cannot be imported from zipfiles.
The default search path is installation dependent, but generally begins with prefix /lib/python version (see PYTHONHOME above). It is always appended to PYTHONPATH .
An additional directory will be inserted in the search path in front of PYTHONPATH as described above under Interface options . The search path can be manipulated from within a Python program as the variable sys.path .
If this is set to a non-empty string, don’t prepend a potentially unsafe path to sys.path : see the -P option for details.
New in version 3.11.
If this is set to a non-empty string, it overrides the sys.platlibdir value.
New in version 3.9.
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 namespace 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 and the hook sys.__interactivehook__ in this file.
Raises an auditing event cpython.run_startup with the filename as the argument when called on startup.
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.
If this is set, it names a callable using dotted-path notation. The module containing the callable will be imported and then the callable will be run by the default implementation of sys.breakpointhook() which itself is called by built-in breakpoint() . If not set, or set to the empty string, it is equivalent to the value “pdb.set_trace”. Setting this to the string “0” causes the default implementation of sys.breakpointhook() to do nothing but return immediately.
New in version 3.7.
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.
If this is set to a non-empty string it is equivalent to specifying the -i option.
This variable can also be modified by Python code using os.environ to force inspect mode on program termination.
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. If set to an integer, it is equivalent to specifying -v multiple times.
If this is set, Python ignores case in import statements. This only works on Windows and macOS.
If this is set to a non-empty string, Python won’t try to write .pyc files on the import of source modules. This is equivalent to specifying the -B option.
If this is set, Python will write .pyc files in a mirror directory tree at this path, instead of in __pycache__ directories within the source tree. This is equivalent to specifying the -X pycache_prefix=PATH option.
New in version 3.8.
If this variable is not set or 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.
New in version 3.2.3.
If this variable is set to an integer, it is used to configure the interpreter’s global integer string conversion length limitation .
New in version 3.11.
If this is set before running the interpreter, it overrides the encoding used for stdin/stdout/stderr, in the syntax encodingname:errorhandler . Both the encodingname and the :errorhandler parts are optional and have the same meaning as in str.encode() .
For stderr, the :errorhandler part is ignored; the handler will always be ‘backslashreplace’ .
Changed in version 3.4: The encodingname part is now optional.
Changed in version 3.6: On Windows, the encoding specified by this variable is ignored for interactive console buffers unless PYTHONLEGACYWINDOWSSTDIO is also specified. Files and pipes redirected through the standard streams are not affected.
If this is set, Python won’t add the user site-packages directory to sys.path .
PEP 370 – Per user site-packages directory
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 .
PEP 370 – Per user site-packages directory
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 macOS.
This is equivalent to the -W option. If set to a comma separated string, it is equivalent to specifying -W multiple times, with filters later in the list taking precedence over those earlier in the list.
The simplest settings apply a particular action unconditionally to all warnings emitted by a process (even those that are otherwise ignored by default):
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 -X faulthandler option.
New in version 3.3.
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. See the tracemalloc.start() for more information.
New in version 3.4.
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.
New in version 3.7.
If this environment variable is set to a non-empty string, enable the debug mode of the asyncio module.
New in version 3.4.
Set the Python memory allocators and/or install debug hooks.
Set the family of memory allocators used by Python:
malloc : use the malloc() function of the C library for all domains ( PYMEM_DOMAIN_RAW , PYMEM_DOMAIN_MEM , PYMEM_DOMAIN_OBJ ).
pymalloc : use the pymalloc allocator for PYMEM_DOMAIN_MEM and PYMEM_DOMAIN_OBJ domains and use the malloc() function for the PYMEM_DOMAIN_RAW domain.
debug : install debug hooks on top of the default memory allocators .
malloc_debug : same as malloc but also install debug hooks.
pymalloc_debug : same as pymalloc but also install debug hooks.
Changed in version 3.7: Added the "default" allocator.
New in version 3.6.
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() allocator of the C library, or if Python is configured without pymalloc support.
Changed in version 3.6: This variable can now also be used on Python compiled in release mode. It now has no effect if set to an empty string.
If set to a non-empty string, the default filesystem encoding and error handler mode will revert to their pre-3.6 values of ‘mbcs’ and ‘replace’, respectively. Otherwise, the new defaults ‘utf-8’ and ‘surrogatepass’ are used.
This may also be enabled at runtime with sys._enablelegacywindowsfsencoding() .
New in version 3.6: See PEP 529 for more details.
If set to a non-empty string, does not use the new console reader and writer. This means that Unicode characters will be encoded according to the active console code page, rather than using utf-8.
This variable is ignored if the standard streams are redirected (to files or pipes) rather than referring to console buffers.
New in version 3.6.
If set to the value 0 , causes the main Python command line application to skip coercing the legacy ASCII-based C and POSIX locales to a more capable UTF-8 based alternative.
If this variable is not set (or is set to a value other than 0 ), the LC_ALL locale override environment variable is also not set, and the current locale reported for the LC_CTYPE category is either the default C locale, or else the explicitly ASCII-based POSIX locale, then the Python CLI will attempt to configure the following locales for the LC_CTYPE category in the order listed before loading the interpreter runtime:
If setting one of these locale categories succeeds, then the LC_CTYPE environment variable will also be set accordingly in the current process environment before the Python runtime is initialized. This ensures that in addition to being seen by both the interpreter itself and other locale-aware components running in the same process (such as the GNU readline library), the updated setting is also seen in 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 via the above implicit locale coercion) automatically enables the surrogateescape error handler for sys.stdin and sys.stdout ( sys.stderr continues to use backslashreplace as it does in any other locale). This stream handling behavior can be overridden using PYTHONIOENCODING as usual.
For debugging purposes, setting PYTHONCOERCECLOCALE=warn will cause Python to emit warning messages on stderr if either the locale coercion activates, or else if a locale that would have triggered coercion is still active when the Python runtime is initialized.
Also note that even when locale coercion is disabled, or when it fails to find a suitable target locale, PYTHONUTF8 will still activate by default in legacy ASCII-based locales. Both features must be disabled in order to force the interpreter to use ASCII instead of UTF-8 for system interfaces.
New in version 3.7: See PEP 538 for more details.
If this environment variable is set to a non-empty string, enable Python Development Mode , introducing additional runtime checks that are too expensive to be enabled by default.
New in version 3.7.
If set to 1 , enable the Python UTF-8 Mode .
If set to 0 , disable the Python UTF-8 Mode .
Setting any other non-empty string causes an error during interpreter initialisation.
New in version 3.7.
If this environment variable is set to a non-empty string, issue a EncodingWarning when the locale-specific default encoding is used.
New in version 3.10.
If this variable is set, it disables the inclusion of the tables mapping extra location information (end line, start column offset and end column offset) to every instruction in code objects. This is useful when smaller code objects and pyc files are desired as well as suppressing the extra visual location indicators when the interpreter displays tracebacks.
New in version 3.11.
1.2.1. Debug-mode variables¶
If set, Python will print threading debug info into stdout.
Deprecated since version 3.10, will be removed in version 3.12.
If set, Python will dump objects and reference counts still alive after shutting down the interpreter.
Need Python configured with the —with-trace-refs build option.
If set, Python will dump objects and reference counts still alive after shutting down the interpreter into a file called FILENAME.
Передача параметров в скрипт Python из командной строки.
При запуске скриптов, часто требуется указать какие-то дополнительные параметры, которые будут использованы в ходе работы программы. Конечно, можно при помощи функции input() получить данные от пользователя и сохранить их в переменных. Как говорится, дело вкуса. Но вместо множественного вызова функции input() есть намного более элегантное решение. Это передача параметров в скрипт python, непосредственно в командной строке — в момент вызова программы. Как это сделать? Давайте разберемся.
Для начала, наберите небольшую программу в своем редакторе. Сохраните её в папке C:\PyScript под именем input_var.py. Разумеется, папку и файл можете назвать как угодно, но тогда не забудьте указать свои данные при вызове скрипта в командной строке.
Как видите, программа очень маленькая. Но её вполне хватит для демонстрации способа передачи данных в скрипт. После того, как следуя приведенным выше инструкциям, вы набрали и сохранили программу, вызовите командную строку Windows. После этого укажите имя интерпретатора python, путь к вызываемому файлу и три значения, разделяя все пробелами, как на рисунке ниже:
Рис. 1 Передача данных в скрипт Python
Если у вас скрипт хранится в другой папке — укажите свой путь к нему. После этого нажмите клавишу Enter на клавиатуре. В результате вы должны увидеть следующее:
Рис. 2 Результат выполнения программы
А теперь давайте разберем, как же это все работает.
Во второй строке мы импортируем argv из модуля sys. Во многих языках переменных argv — стандартное имя. В этой переменной хранятся данных, которые вы передаете сценарию. Пока нам достаточно знать, что эта переменная работает как «контейнер», в котором мы можем передать данные скрипту.
В четвертой строке мы производим «распаковку» содержимого argv в переменные. Слово «распаковка» может показаться странным, но в данном случае оно наиболее подходит. Фактически, мы сообщаем интерпретатору Python, что он должен взять данные из argv и последовательно поместить их в переменные, которые мы указали с левой стороны. После этого мы можем работать с ними как с обычными переменными, которым присвоили значения.
Вы можете указать свои значения вместо «15 два 105», но число значений, которые вы передаете скрипту, должно строго соответствовать количеству переменных, в которые «распаковывается» содержимое argv. Иначе вы увидите сообщение об ошибке:
Рис. 3 Ошибка распаковки данных.
Это сообщение возникло потому что мы передали в скрипт Python недостаточно данных. Если конкретнее, то строка ValueError прямо сообщает, что необходимо 4 значения, но указано 3 (имя скрипта передается автоматически).
Не забывайте, что все данные, которые мы передаем в программу python являются строковыми значениями. Поэтому параметры «10» и «105» сначала необходимо преобразовать в числовой тип при помощи функции int(), а только потом использовать в математических операциях. Будьте внимательны!
Execute a file with arguments in Python shell
I would like to run a command in Python Shell to execute a file with an argument.
For example: execfile(«abc.py») but how to add 2 arguments?
13 Answers 13
Actually, wouldn’t we want to do this?
execfile runs a Python file, but by loading it, not as a script. You can only pass in variable bindings, not arguments.
If you want to run a program from within Python, use subprocess.call . E.g.
Note that when abc.py finishes, control will be returned to the calling program. Note too that abc.py can call quit() if indeed finished.
For more interesting scenarios, you could also look at the runpy module. Since python 2.7, it has the run_path function. E.g:
You’re confusing loading a module into the current interpreter process and calling a Python script externally.
The former can be done by import ing the file you’re interested in. execfile is similar to importing but it simply evaluates the file rather than creates a module out of it. Similar to «sourcing» in a shell script.
The latter can be done using the subprocess module. You spawn off another instance of the interpreter and pass whatever parameters you want to that. This is similar to shelling out in a shell script using backticks.