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<!DOCTYPE html>

<head>

<title>argparse --- Parser for command-line options, arguments and subcommands — مستندات Python3.14.6</title><meta name="viewport" content="width=device-width, initial-scale=1.0">

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<h3><a href="../contents.html">فهرست عناوین</a></h3>

<ul>

<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate">argparse</code> --- Parser for command-line options, arguments and subcommands</a><ul>

<li><a class="reference internal" href="#argumentparser-objects">ArgumentParser objects</a><ul>

<li><a class="reference internal" href="#usage">usage</a></li>

<li><a class="reference internal" href="#description">description</a></li>

<li><a class="reference internal" href="#epilog">epilog</a></li>

<li><a class="reference internal" href="#parents">parents</a></li>

<li><a class="reference internal" href="#formatter-class">formatter_class</a></li>

<li><a class="reference internal" href="#prefix-chars">prefix_chars</a></li>

<li><a class="reference internal" href="#fromfile-prefix-chars">fromfile_prefix_chars</a></li>

<li><a class="reference internal" href="#argument-default">argument_default</a></li>

<li><a class="reference internal" href="#allow-abbrev">allow_abbrev</a></li>

<li><a class="reference internal" href="#conflict-handler">conflict_handler</a></li>

<li><a class="reference internal" href="#exit-on-error">exit_on_error</a></li>

<li><a class="reference internal" href="#suggest-on-error">suggest_on_error</a></li>

<li><a class="reference internal" href="#color">color</a></li>

</ul>

</li>

<li><a class="reference internal" href="#the-add-argument-method">The add_argument() method</a><ul>

<li><a class="reference internal" href="#name-or-flags">name or flags</a></li>

<li><a class="reference internal" href="#action">action</a></li>

<li><a class="reference internal" href="#nargs">nargs</a></li>

<li><a class="reference internal" href="#const">const</a></li>

<li><a class="reference internal" href="#default">default</a></li>

<li><a class="reference internal" href="#choices">choices</a></li>

<li><a class="reference internal" href="#required">required</a></li>

<li><a class="reference internal" href="#metavar">metavar</a></li>

<li><a class="reference internal" href="#deprecated">deprecated</a></li>

<li><a class="reference internal" href="#action-classes">Action classes</a></li>

</ul>

</li>

<li><a class="reference internal" href="#the-parse-args-method">The parse_args() method</a><ul>

<li><a class="reference internal" href="#option-value-syntax">Option value syntax</a></li>

<li><a class="reference internal" href="#invalid-arguments">Invalid arguments</a></li>

<li><a class="reference internal" href="#arguments-containing">Arguments containing <code class="docutils literal notranslate">-</code></a></li>

<li><a class="reference internal" href="#argument-abbreviations-prefix-matching">Argument abbreviations (prefix matching)</a></li>

<li><a class="reference internal" href="#beyond-sys-argv">Beyond <code class="docutils literal notranslate">sys.argv</code></a></li>

<li><a class="reference internal" href="#the-namespace-object">The Namespace object</a></li>

</ul>

</li>

<li><a class="reference internal" href="#other-utilities">Other utilities</a><ul>

<li><a class="reference internal" href="#subcommands">Subcommands</a></li>

<li><a class="reference internal" href="#filetype-objects">FileType objects</a></li>

<li><a class="reference internal" href="#argument-groups">Argument groups</a></li>

<li><a class="reference internal" href="#mutual-exclusion">Mutual exclusion</a></li>

<li><a class="reference internal" href="#parser-defaults">Parser defaults</a></li>

<li><a class="reference internal" href="#printing-help">Printing help</a></li>

<li><a class="reference internal" href="#partial-parsing">Partial parsing</a></li>

<li><a class="reference internal" href="#customizing-file-parsing">Customizing file parsing</a></li>

<li><a class="reference internal" href="#exiting-methods">Exiting methods</a></li>

<li><a class="reference internal" href="#intermixed-parsing">Intermixed parsing</a></li>

<li><a class="reference internal" href="#registering-custom-types-or-actions">Registering custom types or actions</a></li>

</ul>

</li>

<li><a class="reference internal" href="#exceptions">Exceptions</a></li>

</ul>

</li>

</ul>

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<div>

<h4>موضوع قبلی</h4>

<a href="cmdlinelibs.html"

title="فصل قبلی">Command-line interface libraries</a>

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<h4>موضوع بعدی</h4>

<a href="../howto/argparse.html"

title="فصل بعدی">Argparse Tutorial</a>

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<li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate">argparse</code> --- Parser for command-line options, arguments and subcommands</a></li>

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<h1><code class="xref py py-mod docutils literal notranslate">argparse</code> --- Parser for command-line options, arguments and subcommands<a class="headerlink" href="#module-argparse" title="Link to this heading">¶</a></h1>

Added in version 3.2.

</div>

Source code: <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.14/Lib/argparse.py">Lib/argparse.py</a>

توجه

While <code class="xref py py-mod docutils literal notranslate">argparse</code> is the default recommended standard library module

for implementing basic command line applications, authors with more

exacting requirements for exactly how their command line applications

behave may find it doesn't provide the necessary level of control.

Refer to <a class="reference internal" href="optparse.html#choosing-an-argument-parser">Choosing an argument parsing library</a> for alternatives to

consider when <code class="docutils literal notranslate">argparse</code> doesn't support behaviors that the application

requires (such as entirely disabling support for interspersed options and

positional arguments, or accepting option parameter values that start

with <code class="docutils literal notranslate">-</code> even when they correspond to another defined option).

</div>

Tutorial

This page contains the API reference information. For a more gentle

introduction to Python command-line parsing, have a look at the

<a class="reference internal" href="../howto/argparse.html#argparse-tutorial">argparse tutorial</a>.

</aside>

The <code class="xref py py-mod docutils literal notranslate">argparse</code> module makes it easy to write user-friendly command-line

interfaces. The program defines what arguments it requires, and <code class="xref py py-mod docutils literal notranslate">argparse</code>

will figure out how to parse those out of <a class="reference internal" href="sys.html#sys.argv" title="sys.argv"><code class="xref py py-data docutils literal notranslate">sys.argv</code></a>. The <code class="xref py py-mod docutils literal notranslate">argparse</code>

module also automatically generates help and usage messages. The module

will also issue errors when users give the program invalid arguments.

The <code class="xref py py-mod docutils literal notranslate">argparse</code> module's support for command-line interfaces is built

around an instance of <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">argparse.ArgumentParser</code></a>. It is a container for

argument specifications and has options that apply to the parser as whole:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>parser = argparse.ArgumentParser(

prog='ProgramName',

description='What the program does',

epilog='Text at the bottom of help')

</pre></div>

</div>

The <a class="reference internal" href="#argparse.ArgumentParser.add_argument" title="argparse.ArgumentParser.add_argument"><code class="xref py py-meth docutils literal notranslate">ArgumentParser.add_argument()</code></a> method attaches individual argument

specifications to the parser. It supports positional arguments, options that

accept values, and on/off flags:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>parser.add_argument('filename') # positional argument

parser.add_argument('-c', '--count') # option that takes a value

parser.add_argument('-v', '--verbose',

action='store_true') # on/off flag

</pre></div>

</div>

The <a class="reference internal" href="#argparse.ArgumentParser.parse_args" title="argparse.ArgumentParser.parse_args"><code class="xref py py-meth docutils literal notranslate">ArgumentParser.parse_args()</code></a> method runs the parser and places

the extracted data in a <a class="reference internal" href="#argparse.Namespace" title="argparse.Namespace"><code class="xref py py-class docutils literal notranslate">argparse.Namespace</code></a> object:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>args = parser.parse_args()

print(args.filename, args.count, args.verbose)

</pre></div>

</div>

توجه

If you're looking for a guide about how to upgrade <a class="reference internal" href="optparse.html#module-optparse" title="optparse: Command-line option parsing library."><code class="xref py py-mod docutils literal notranslate">optparse</code></a> code

to <code class="xref py py-mod docutils literal notranslate">argparse</code>, see <a class="reference internal" href="../howto/argparse-optparse.html#upgrading-optparse-code">Upgrading Optparse Code</a>.

</div>

<h2>ArgumentParser objects<a class="headerlink" href="#argumentparser-objects" title="Link to this heading">¶</a></h2>

class argparse.ArgumentParser(prog=None, usage=None, description=None, epilog=None, parents=[], formatter_class=argparse.HelpFormatter, prefix_chars='-', fromfile_prefix_chars=None, argument_default=None, conflict_handler='error', add_help=True, allow_abbrev=True, exit_on_error=True, <abbr title="Keyword-only parameters separator (PEP 3102)">*</abbr>, suggest_on_error=False, color=True)<a class="headerlink" href="#argparse.ArgumentParser" title="Link to this definition">¶</a></dt>

<dd>Create a new <code class="xref py py-class docutils literal notranslate">ArgumentParser</code> object. All parameters should be passed

as keyword arguments. Each parameter has its own more detailed description

below, but in short they are:

<li><a class="reference internal" href="#prog">prog</a> - The name of the program (default: generated from the <code class="docutils literal notranslate">__main__</code>

module attributes and <code class="docutils literal notranslate">sys.argv[0]</code>)</li>

<li><a class="reference internal" href="#usage">usage</a> - The string describing the program usage (default: generated from

arguments added to parser)</li>

<li><a class="reference internal" href="#description">description</a> - Text to display before the argument help

(by default, no text)</li>

<li><a class="reference internal" href="#epilog">epilog</a> - Text to display after the argument help (by default, no text)</li>

<li><a class="reference internal" href="#parents">parents</a> - A list of <code class="xref py py-class docutils literal notranslate">ArgumentParser</code> objects whose arguments should

also be included</li>

<li><a class="reference internal" href="#formatter-class">formatter_class</a> - A class for customizing the help output</li>

<li><a class="reference internal" href="#prefix-chars">prefix_chars</a> - The set of characters that prefix optional arguments

(default: '-')</li>

<li><a class="reference internal" href="#fromfile-prefix-chars">fromfile_prefix_chars</a> - The set of characters that prefix files from

which additional arguments should be read (default: <code class="docutils literal notranslate">None</code>)</li>

<li><a class="reference internal" href="#argument-default">argument_default</a> - The global default value for arguments

(default: <code class="docutils literal notranslate">None</code>)</li>

<li><a class="reference internal" href="#conflict-handler">conflict_handler</a> - The strategy for resolving conflicting optionals

(usually unnecessary)</li>

<li><a class="reference internal" href="#add-help">add_help</a> - Add a <code class="docutils literal notranslate">-h/--help</code> option to the parser (default: <code class="docutils literal notranslate">True</code>)</li>

<li><a class="reference internal" href="#allow-abbrev">allow_abbrev</a> - Allows long options to be abbreviated if the

abbreviation is unambiguous (default: <code class="docutils literal notranslate">True</code>)</li>

<li><a class="reference internal" href="#exit-on-error">exit_on_error</a> - Determines whether or not <code class="xref py py-class docutils literal notranslate">ArgumentParser</code> exits with

error info when an error occurs. (default: <code class="docutils literal notranslate">True</code>)</li>

<li><a class="reference internal" href="#suggest-on-error">suggest_on_error</a> - Enables suggestions for mistyped argument choices

and subparser names (default: <code class="docutils literal notranslate">False</code>)</li>

<li><a class="reference internal" href="#color">color</a> - Allow color output (default: <code class="docutils literal notranslate">True</code>)</li>

</ul>

تغییر داده شده در نسخه 3.5: allow_abbrev parameter was added.

</div>

تغییر داده شده در نسخه 3.8: In previous versions, allow_abbrev also disabled grouping of short

flags such as <code class="docutils literal notranslate">-vv</code> to mean <code class="docutils literal notranslate">-v -v</code>.

</div>

تغییر داده شده در نسخه 3.9: exit_on_error parameter was added.

</div>

تغییر داده شده در نسخه 3.14: suggest_on_error and color parameters were added.

</div>

</dd></dl>

The following sections describe how each of these are used.

By default, <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a> calculates the name of the program

to display in help messages depending on the way the Python interpreter was run:

<li>The <a class="reference internal" href="os.path.html#os.path.basename" title="os.path.basename"><code class="xref py py-func docutils literal notranslate">base name</code></a> of <code class="docutils literal notranslate">sys.argv[0]</code> if a file was

passed as argument.</li>

<li>The Python interpreter name followed by <code class="docutils literal notranslate">sys.argv[0]</code> if a directory or

a zipfile was passed as argument.</li>

<li>The Python interpreter name followed by <code class="docutils literal notranslate">-m</code> followed by the

module or package name if the <a class="reference internal" href="../using/cmdline.html#cmdoption-m"><code class="xref std std-option docutils literal notranslate">-m</code></a> option was used.</li>

</ul>

This default is almost always desirable because it will make the help messages

match the string that was used to invoke the program on the command line.

However, to change this default behavior, another value can be supplied using

the <code class="docutils literal notranslate">prog=</code> argument to <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a>:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> parser = argparse.ArgumentParser(prog='myprogram')

>>> parser.print_help()

usage: myprogram [-h]

options:

-h, --help show this help message and exit

</pre></div>

</div>

Note that the program name, whether determined from <code class="docutils literal notranslate">sys.argv[0]</code>,

from the <code class="docutils literal notranslate">__main__</code> module attributes or from the

<code class="docutils literal notranslate">prog=</code> argument, is available to help messages using the <code class="docutils literal notranslate">%(prog)s</code> format

specifier.

>>> parser.print_help()

usage: myprogram [-h] [--foo FOO]

options:

-h, --help show this help message and exit

--foo FOO foo of the myprogram program

</pre></div>

</div>

تغییر داده شده در نسخه 3.14: The default <code class="docutils literal notranslate">prog</code> value now reflects how <code class="docutils literal notranslate">__main__</code> was actually executed,

rather than always being <code class="docutils literal notranslate">os.path.basename(sys.argv[0])</code>.

</div>

</section>

<h3>usage<a class="headerlink" href="#usage" title="Link to this heading">¶</a></h3>

arguments it contains. The default message can be overridden with the

<code class="docutils literal notranslate">usage=</code> keyword argument:

>>> parser.print_help()

usage: PROG [options]

positional arguments:

bar bar help

options:

-h, --help show this help message and exit

--foo [FOO] foo help

</pre></div>

</div>

The <code class="docutils literal notranslate">%(prog)s</code> format specifier is available to fill in the program name in

your usage messages.

When a custom usage message is specified for the main parser, you may also want to

consider passing the <code class="docutils literal notranslate">prog</code> argument to <a class="reference internal" href="#argparse.ArgumentParser.add_subparsers" title="argparse.ArgumentParser.add_subparsers"><code class="xref py py-meth docutils literal notranslate">add_subparsers()</code></a>

or the <code class="docutils literal notranslate">prog</code> and the <code class="docutils literal notranslate">usage</code> arguments to

<code class="xref py py-meth docutils literal notranslate">add_parser()</code>, to ensure consistent command prefixes and

usage information across subparsers.

</section>

<h3>description<a class="headerlink" href="#description" title="Link to this heading">¶</a></h3>

Most calls to the <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a> constructor will use the

<code class="docutils literal notranslate">description=</code> keyword argument. This argument gives a brief description of

what the program does and how it works. In help messages, the description is

displayed between the command-line usage string and the help messages for the

various arguments.

By default, the description will be line-wrapped so that it fits within the

given space. To change this behavior, see the <a class="reference internal" href="#formatter-class">formatter_class</a> argument.

</section>

<h3>epilog<a class="headerlink" href="#epilog" title="Link to this heading">¶</a></h3>

Some programs like to display additional description of the program after the

description of the arguments. Such text can be specified using the <code class="docutils literal notranslate">epilog=</code>

argument to <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a>:

... description='A foo that bars',

... epilog="And that's how you'd foo a bar")

>>> parser.print_help()

usage: argparse.py [-h]

A foo that bars

options:

-h, --help show this help message and exit

And that's how you'd foo a bar

</pre></div>

</div>

As with the <a class="reference internal" href="#description">description</a> argument, the <code class="docutils literal notranslate">epilog=</code> text is by default

line-wrapped, but this behavior can be adjusted with the <a class="reference internal" href="#formatter-class">formatter_class</a>

</section>

<h3>parents<a class="headerlink" href="#parents" title="Link to this heading">¶</a></h3>

Sometimes, several parsers share a common set of arguments. Rather than

repeating the definitions of these arguments, a single parser with all the

shared arguments and passed to <code class="docutils literal notranslate">parents=</code> argument to <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a>

can be used. The <code class="docutils literal notranslate">parents=</code> argument takes a list of <code class="xref py py-class docutils literal notranslate">ArgumentParser</code>

objects, collects all the positional and optional actions from them, and adds

these actions to the <code class="xref py py-class docutils literal notranslate">ArgumentParser</code> object being constructed:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> parent_parser = argparse.ArgumentParser(add_help=False)

>>> parent_parser.add_argument('--parent', type=int)

>>> foo_parser = argparse.ArgumentParser(parents=[parent_parser])

>>> foo_parser.add_argument('foo')

>>> foo_parser.parse_args(['--parent', '2', 'XXX'])

Namespace(foo='XXX', parent=2)

>>> bar_parser = argparse.ArgumentParser(parents=[parent_parser])

>>> bar_parser.add_argument('--bar')

>>> bar_parser.parse_args(['--bar', 'YYY'])

Namespace(bar='YYY', parent=None)

</pre></div>

</div>

Note that most parent parsers will specify <code class="docutils literal notranslate">add_help=False</code>. Otherwise, the

<a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a> will see two <code class="docutils literal notranslate">-h/--help</code> options (one in the parent

and one in the child) and raise an error.

توجه

You must fully initialize the parsers before passing them via <code class="docutils literal notranslate">parents=</code>.

If you change the parent parsers after the child parser, those changes will

not be reflected in the child.

</div>

</section>

<h3>formatter_class<a class="headerlink" href="#formatter-class" title="Link to this heading">¶</a></h3>

specifying an alternate formatting class. Currently, there are four such

classes:

<a class="reference internal" href="#argparse.RawDescriptionHelpFormatter" title="argparse.RawDescriptionHelpFormatter"><code class="xref py py-class docutils literal notranslate">RawDescriptionHelpFormatter</code></a> and <a class="reference internal" href="#argparse.RawTextHelpFormatter" title="argparse.RawTextHelpFormatter"><code class="xref py py-class docutils literal notranslate">RawTextHelpFormatter</code></a> give

more control over how textual descriptions are displayed.

By default, <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a> objects line-wrap the <a class="reference internal" href="#description">description</a> and

<a class="reference internal" href="#epilog">epilog</a> texts in command-line help messages:

... prog='PROG',

... description='''this description

... was indented weird

... but that is okay''',

... epilog='''

... likewise for this epilog whose whitespace will

... be cleaned up and whose words will be wrapped

... across a couple lines''')

>>> parser.print_help()

usage: PROG [-h]

this description was indented weird but that is okay

options:

-h, --help show this help message and exit

likewise for this epilog whose whitespace will be cleaned up and whose words

will be wrapped across a couple lines

</pre></div>

</div>

Passing <a class="reference internal" href="#argparse.RawDescriptionHelpFormatter" title="argparse.RawDescriptionHelpFormatter"><code class="xref py py-class docutils literal notranslate">RawDescriptionHelpFormatter</code></a> as <code class="docutils literal notranslate">formatter_class=</code>

indicates that <a class="reference internal" href="#description">description</a> and <a class="reference internal" href="#epilog">epilog</a> are already correctly formatted and

should not be line-wrapped:

... prog='PROG',

... formatter_class=argparse.RawDescriptionHelpFormatter,

... description=textwrap.dedent('''\

... Please do not mess up this text!

... --------------------------------

... I have indented it

... exactly the way

... I want it

... '''))

>>> parser.print_help()

usage: PROG [-h]

Please do not mess up this text!

--------------------------------

I have indented it

exactly the way

I want it

options:

-h, --help show this help message and exit

</pre></div>

</div>

<a class="reference internal" href="#argparse.RawTextHelpFormatter" title="argparse.RawTextHelpFormatter"><code class="xref py py-class docutils literal notranslate">RawTextHelpFormatter</code></a> maintains whitespace for all sorts of help text,

including argument descriptions. However, multiple newlines are replaced with

one. If you wish to preserve multiple blank lines, add spaces between the

newlines.

<a class="reference internal" href="#argparse.ArgumentDefaultsHelpFormatter" title="argparse.ArgumentDefaultsHelpFormatter"><code class="xref py py-class docutils literal notranslate">ArgumentDefaultsHelpFormatter</code></a> automatically adds information about

default values to each of the argument help messages:

... prog='PROG',

... formatter_class=argparse.ArgumentDefaultsHelpFormatter)

>>> parser.add_argument('--foo', type=int, default=42, help='FOO!')

>>> parser.add_argument('bar', nargs='*', default=[1, 2, 3], help='BAR!')

>>> parser.print_help()

usage: PROG [-h] [--foo FOO] [bar ...]

positional arguments:

bar BAR! (default: [1, 2, 3])

options:

-h, --help show this help message and exit

--foo FOO FOO! (default: 42)

</pre></div>

</div>

<a class="reference internal" href="#argparse.MetavarTypeHelpFormatter" title="argparse.MetavarTypeHelpFormatter"><code class="xref py py-class docutils literal notranslate">MetavarTypeHelpFormatter</code></a> uses the name of the <a class="reference internal" href="#type">type</a> argument for each

argument as the display name for its values (rather than using the <a class="reference internal" href="#dest">dest</a>

as the regular formatter does):

... prog='PROG',

... formatter_class=argparse.MetavarTypeHelpFormatter)

>>> parser.print_help()

usage: PROG [-h] [--foo int] float

positional arguments:

float

options:

-h, --help show this help message and exit

--foo int

</pre></div>

</div>

</section>

<h3>prefix_chars<a class="headerlink" href="#prefix-chars" title="Link to this heading">¶</a></h3>

Most command-line options will use <code class="docutils literal notranslate">-</code> as the prefix, e.g. <code class="docutils literal notranslate">-f/--foo</code>.

Parsers that need to support different or additional prefix

characters, e.g. for options

like <code class="docutils literal notranslate">+f</code> or <code class="docutils literal notranslate">/foo</code>, may specify them using the <code class="docutils literal notranslate">prefix_chars=</code> argument

to the <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a> constructor:

>>> parser.add_argument('+f')

>>> parser.add_argument('++bar')

>>> parser.parse_args('+f X ++bar Y'.split())

Namespace(bar='Y', f='X')

</pre></div>

</div>

The <code class="docutils literal notranslate">prefix_chars=</code> argument defaults to <code class="docutils literal notranslate">'-'</code>. Supplying a set of

characters that does not include <code class="docutils literal notranslate">-</code> will cause <code class="docutils literal notranslate">-f/--foo</code> options to be

disallowed.

</section>

<h3>fromfile_prefix_chars<a class="headerlink" href="#fromfile-prefix-chars" title="Link to this heading">¶</a></h3>

Sometimes, when dealing with a particularly long argument list, it

may make sense to keep the list of arguments in a file rather than typing it out

at the command line. If the <code class="docutils literal notranslate">fromfile_prefix_chars=</code> argument is given to the

<a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a> constructor, then arguments that start with any of the

specified characters will be treated as files, and will be replaced by the

arguments they contain. For example:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> with open('args.txt', 'w', encoding=sys.getfilesystemencoding()) as fp:

... fp.write('-f\nbar')

...

>>> parser = argparse.ArgumentParser(fromfile_prefix_chars='@')

>>> parser.add_argument('-f')

>>> parser.parse_args(['-f', 'foo', '@args.txt'])

Namespace(f='bar')

</pre></div>

</div>

Arguments read from a file must be one per line by default (but see also

<a class="reference internal" href="#argparse.ArgumentParser.convert_arg_line_to_args" title="argparse.ArgumentParser.convert_arg_line_to_args"><code class="xref py py-meth docutils literal notranslate">convert_arg_line_to_args()</code></a>) and are treated as if they

were in the same place as the original file referencing argument on the command

line. So in the example above, the expression <code class="docutils literal notranslate">['-f', 'foo', '@args.txt']</code>

is considered equivalent to the expression <code class="docutils literal notranslate">['-f', 'foo', '-f', 'bar']</code>.

توجه

Each line is treated as a single argument, so an empty line is read as an

empty string (<code class="docutils literal notranslate">''</code>).

</div>

<a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a> uses <a class="reference internal" href="../glossary.html#term-filesystem-encoding-and-error-handler">filesystem encoding and error handler</a>

to read the file containing arguments.

The <code class="docutils literal notranslate">fromfile_prefix_chars=</code> argument defaults to <code class="docutils literal notranslate">None</code>, meaning that

arguments will never be treated as file references.

تغییر داده شده در نسخه 3.12: <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a> changed encoding and errors to read arguments files

from default (e.g. <a class="reference internal" href="locale.html#locale.getpreferredencoding" title="locale.getpreferredencoding"><code class="xref py py-func docutils literal notranslate">locale.getpreferredencoding(False)</code></a>

and <code class="docutils literal notranslate">"strict"</code>) to the <a class="reference internal" href="../glossary.html#term-filesystem-encoding-and-error-handler">filesystem encoding and error handler</a>.

Arguments file should be encoded in UTF-8 instead of ANSI Codepage on Windows.

</div>

</section>

<h3>argument_default<a class="headerlink" href="#argument-default" title="Link to this heading">¶</a></h3>

Generally, argument defaults are specified either by passing a default to

<a class="reference internal" href="#argparse.ArgumentParser.add_argument" title="argparse.ArgumentParser.add_argument"><code class="xref py py-meth docutils literal notranslate">add_argument()</code></a> or by calling the

<a class="reference internal" href="#argparse.ArgumentParser.set_defaults" title="argparse.ArgumentParser.set_defaults"><code class="xref py py-meth docutils literal notranslate">set_defaults()</code></a> methods with a specific set of name-value

pairs. Sometimes however, it may be useful to specify a single parser-wide

default for arguments. This can be accomplished by passing the

<code class="docutils literal notranslate">argument_default=</code> keyword argument to <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a>. For example,

to globally suppress attribute creation on <a class="reference internal" href="#argparse.ArgumentParser.parse_args" title="argparse.ArgumentParser.parse_args"><code class="xref py py-meth docutils literal notranslate">parse_args()</code></a>

calls, we supply <code class="docutils literal notranslate">argument_default=SUPPRESS</code>:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> parser = argparse.ArgumentParser(argument_default=argparse.SUPPRESS)

>>> parser.add_argument('--foo')

>>> parser.parse_args(['--foo', '1', 'BAR'])

Namespace(bar='BAR', foo='1')

>>> parser.parse_args([])

Namespace()

</pre></div>

</div>

</section>

<h3>allow_abbrev<a class="headerlink" href="#allow-abbrev" title="Link to this heading">¶</a></h3>

Normally, when you pass an argument list to the

<a class="reference internal" href="#argparse.ArgumentParser.parse_args" title="argparse.ArgumentParser.parse_args"><code class="xref py py-meth docutils literal notranslate">parse_args()</code></a> method of an <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a>,

it <a class="reference internal" href="#prefix-matching">recognizes abbreviations</a> of long options.

This feature can be disabled by setting <code class="docutils literal notranslate">allow_abbrev</code> to <code class="docutils literal notranslate">False</code>:

>>> parser.parse_args(['--foon'])

usage: PROG [-h] [--foobar] [--foonley]

PROG: error: unrecognized arguments: --foon

</pre></div>

</div>

Added in version 3.5.

</div>

</section>

<h3>conflict_handler<a class="headerlink" href="#conflict-handler" title="Link to this heading">¶</a></h3>

string. By default, <code class="xref py py-class docutils literal notranslate">ArgumentParser</code> objects raise an exception if an

attempt is made to create an argument with an option string that is already in

use:

Traceback (most recent call last):

..

ArgumentError: argument --foo: conflicting option string(s): --foo

</pre></div>

</div>

Sometimes (e.g. when using <a class="reference internal" href="#parents">parents</a>) it may be useful to simply override any

older arguments with the same option string. To get this behavior, the value

<code class="docutils literal notranslate">'resolve'</code> can be supplied to the <code class="docutils literal notranslate">conflict_handler=</code> argument of

>>> parser.print_help()

usage: PROG [-h] [-f FOO] [--foo FOO]

options:

-h, --help show this help message and exit

-f FOO old foo help

--foo FOO new foo help

</pre></div>

</div>

Note that <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a> objects only remove an action if all of its

option strings are overridden. So, in the example above, the old <code class="docutils literal notranslate">-f/--foo</code>

action is retained as the <code class="docutils literal notranslate">-f</code> action, because only the <code class="docutils literal notranslate">--foo</code> option

string was overridden.

</section>

the parser's help message. If <code class="docutils literal notranslate">-h</code> or <code class="docutils literal notranslate">--help</code> is supplied at the command

line, the <code class="xref py py-class docutils literal notranslate">ArgumentParser</code> help will be printed.

Occasionally, it may be useful to disable the addition of this help option.

This can be achieved by passing <code class="docutils literal notranslate">False</code> as the <code class="docutils literal notranslate">add_help=</code> argument to

>>> parser.print_help()

usage: PROG [--foo FOO]

options:

--foo FOO foo help

</pre></div>

</div>

The help option is typically <code class="docutils literal notranslate">-h/--help</code>. The exception to this is

if the <code class="docutils literal notranslate">prefix_chars=</code> is specified and does not include <code class="docutils literal notranslate">-</code>, in

which case <code class="docutils literal notranslate">-h</code> and <code class="docutils literal notranslate">--help</code> are not valid options. In

this case, the first character in <code class="docutils literal notranslate">prefix_chars</code> is used to prefix

the help options:

>>> parser.print_help()

usage: PROG [+h]

options:

+h, ++help show this help message and exit

</pre></div>

</div>

</section>

<h3>exit_on_error<a class="headerlink" href="#exit-on-error" title="Link to this heading">¶</a></h3>

Normally, when you pass an invalid argument list to the <a class="reference internal" href="#argparse.ArgumentParser.parse_args" title="argparse.ArgumentParser.parse_args"><code class="xref py py-meth docutils literal notranslate">parse_args()</code></a>

method of an <a class="reference internal" href="#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">ArgumentParser</code></a>, it will print a message to <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate">sys.stderr</code></a> and exit with a status

code of 2.

If the user would like to catch errors manually, the feature can be enabled by setting

<code class="docutils literal notranslate">exit_on_error</code> to <code class="docutils literal notranslate">False</code>:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> parser = argparse.ArgumentParser(exit_on_error=False)

_StoreAction(option_strings=['--integers'], dest='integers', nargs=None, const=None, default=None, type=<class 'int'>, choices=None, help=None, metavar=None)

>>> try:

... parser.parse_args('--integers a'.split())

... except argparse.ArgumentError:

... print('Catching an argumentError')

...

Catching an argumentError

</pre></div>

</div>

Added in version 3.9.

</div>

</section>

<h3>suggest_on_error<a class="headerlink" href="#suggest-on-error" title="Link to this heading">¶</a></h3>

By default, when a user passes an invalid argument choice or subparser name,

argument choices (if specified) or subparser names as part of the error message.

If the user would like to enable suggestions for mistyped argument choices and

subparser names, the feature can be enabled by setting <code class="docutils literal notranslate">suggest_on_error</code> to

<code class="docutils literal notranslate">True</code>. Note that this only applies for arguments when the choices specified

are strings:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> parser = argparse.ArgumentParser(suggest_on_error=True)

>>> parser.parse_args(['--action', 'debugg'])

usage: tester.py [-h] [--action {debug,dryrun}]

tester.py: error: argument --action: invalid choice: 'debugg', maybe you meant 'debug'? (choose from debug, dryrun)

</pre></div>

</div>

If you're writing code that needs to be compatible with older Python versions

and want to opportunistically use <code class="docutils literal notranslate">suggest_on_error</code> when it's available, you

can set it as an attribute after initializing the parser instead of using the

keyword argument:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> parser = argparse.ArgumentParser(description='Process some integers.')

>>> parser.suggest_on_error = True

</pre></div>

</div>

Added in version 3.14.

</div>

</section>

<h3>color<a class="headerlink" href="#color" title="Link to this heading">¶</a></h3>

By default, the help message is printed in color using <a class="reference external" href="https://en.wikipedia.org/wiki/ANSI_escape_code">ANSI escape sequences</a>.

If you want plain text help messages, you can disable this <a class="reference internal" href="../using/cmdline.html#using-on-controlling-color">in your local

environment</a>, or in the argument parser itself

by setting <code class="docutils literal notranslate">color</code> to <code class="docutils literal notranslate">False</code>:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> parser = argparse.ArgumentParser(description='Process some integers.',

... color=False)

>>> parser.add_argument('integers', metavar='N', type=int, nargs='+',

... help='an integer for the accumulator')

>>> parser.parse_args(['--help'])

</pre></div>

</div>

Note that when <code class="docutils literal notranslate">color=True</code>, colored output depends on both environment

variables and terminal capabilities. However, if <code class="docutils literal notranslate">color=False</code>, colored

output is always disabled, even if environment variables like <code class="docutils literal notranslate">FORCE_COLOR</code>

are set.

توجه

Error messages will include color codes when redirecting stderr to a

file. To avoid this, set the <a class="reference external" href="https://no-color.org/"><code class="docutils literal notranslate">NO_COLOR</code></a> or <a class="reference internal" href="../using/cmdline.html#envvar-PYTHON_COLORS"><code class="xref std std-envvar docutils literal notranslate">PYTHON_COLORS</code></a>

environment variable (for example,

<code class="docutils literal notranslate">NO_COLOR=1 python script.py 2> errors.txt</code>).

</div>

Added in version 3.14.

</div>

</section>

<h2>The add_argument() method<a class="headerlink" href="#the-add-argument-method" title="Link to this heading">¶</a></h2>

ArgumentParser.add_argument(name or flags..., *[, action][, nargs][, const][, default][, type][, choices][, required][, help][, metavar][, dest][, deprecated])<a class="headerlink" href="#argparse.ArgumentParser.add_argument" title="Link to this definition">¶</a></dt>

<dd>Define how a single command-line argument should be parsed. Each parameter

has its own more detailed description below, but in short they are:

<li><a class="reference internal" href="#name-or-flags">name or flags</a> - Either a name or a list of option strings, e.g. <code class="docutils literal notranslate">'foo'</code>

or <code class="docutils literal notranslate">'-f', '--foo'</code>.</li>

<li><a class="reference internal" href="#action">action</a> - The basic type of action to be taken when this argument is

encountered at the command line.</li>

<li><a class="reference internal" href="#nargs">nargs</a> - The number of command-line arguments that should be consumed.</li>

<li><a class="reference internal" href="#const">const</a> - A constant value required by some <a class="reference internal" href="#action">action</a> and <a class="reference internal" href="#nargs">nargs</a> selections.</li>

<li><a class="reference internal" href="#default">default</a> - The value produced if the argument is absent from the

command line and if it is absent from the namespace object.</li>

<li><a class="reference internal" href="#type">type</a> - The type to which the command-line argument should be converted.</li>

<li><a class="reference internal" href="#choices">choices</a> - A sequence of the allowable values for the argument.</li>

<li><a class="reference internal" href="#required">required</a> - Whether or not the command-line option may be omitted

(optionals only).</li>

<li><a class="reference internal" href="#help">help</a> - A brief description of what the argument does.</li>

<li><a class="reference internal" href="#metavar">metavar</a> - A name for the argument in usage messages.</li>

<li><a class="reference internal" href="#dest">dest</a> - The name of the attribute to be added to the object returned by

<li><a class="reference internal" href="#deprecated">deprecated</a> - Whether or not use of the argument is deprecated.</li>

</ul>

The method returns an <a class="reference internal" href="#argparse.Action" title="argparse.Action"><code class="xref py py-class docutils literal notranslate">Action</code></a> object representing the argument.

</dd></dl>

The following sections describe how each of these are used.

<h3>name or flags<a class="headerlink" href="#name-or-flags" title="Link to this heading">¶</a></h3>

The <a class="reference internal" href="#argparse.ArgumentParser.add_argument" title="argparse.ArgumentParser.add_argument"><code class="xref py py-meth docutils literal notranslate">add_argument()</code></a> method must know whether an optional

argument, like <code class="docutils literal notranslate">-f</code> or <code class="docutils literal notranslate">--foo</code>, or a positional argument, like a list of

filenames, is expected. The first arguments passed to

<code class="xref py py-meth docutils literal notranslate">add_argument()</code> must therefore be either a series of

flags, or a simple argument name.

For example, an optional argument could be created like:

</pre></div>

</div>

while a positional argument could be created like:

</pre></div>

</div>

When <a class="reference internal" href="#argparse.ArgumentParser.parse_args" title="argparse.ArgumentParser.parse_args"><code class="xref py py-meth docutils literal notranslate">parse_args()</code></a> is called, optional arguments will be

identified by the <code class="docutils literal notranslate">-</code> prefix, and the remaining arguments will be assumed to

be positional:

>>> parser.add_argument('bar')

>>> parser.parse_args(['BAR'])

Namespace(bar='BAR', foo=None)

>>> parser.parse_args(['BAR', '--foo', 'FOO'])

Namespace(bar='BAR', foo='FOO')

>>> parser.parse_args(['--foo', 'FOO'])

usage: PROG [-h] [-f FOO] bar

PROG: error: the following arguments are required: bar

</pre></div>

</div>

By default, <code class="xref py py-mod docutils literal notranslate">argparse</code> automatically handles the internal naming and

display names of arguments, simplifying the process without requiring

additional configuration.

As such, you do not need to specify the <a class="reference internal" href="#dest">dest</a> and <a class="reference internal" href="#metavar">metavar</a> parameters.

For optional arguments, the <a class="reference internal" href="#dest">dest</a> parameter defaults to the argument name, with

underscores <code class="docutils literal notranslate">_</code> replacing hyphens <code class="docutils literal notranslate">-</code>. The <a class="reference internal" href="#metavar">metavar</a> parameter defaults to

the upper-cased name. For example:

>>> parser.add_argument('--foo-bar')

>>> parser.parse_args(['--foo-bar', 'FOO-BAR'])

Namespace(foo_bar='FOO-BAR')

>>> parser.print_help()

usage: [-h] [--foo-bar FOO-BAR]

optional arguments:

-h, --help show this help message and exit

--foo-bar FOO-BAR

</pre></div>

</div>

</section>

<h3>action<a class="headerlink" href="#action" title="Link to this heading">¶</a></h3>

actions can do just about anything with the command-line arguments associated with

them, though most actions simply add an attribute to the object returned by

<a class="reference internal" href="#argparse.ArgumentParser.parse_args" title="argparse.ArgumentParser.parse_args"><code class="xref py py-meth docutils literal notranslate">parse_args()</code></a>. The <code class="docutils literal notranslate">action</code> keyword argument specifies

how the command-line arguments should be handled. The supplied actions are:

<ul>

<li><code class="docutils literal notranslate">'store'</code> - This just stores the argument's value. This is the default

action.</li>

<li><code class="docutils literal notranslate">'store_const'</code> - This stores the value specified by the <a class="reference internal" href="#const">const</a> keyword

argument; note that the <a class="reference internal" href="#const">const</a> keyword argument defaults to <code class="docutils literal notranslate">None</code>. The

<code class="docutils literal notranslate">'store_const'</code> action is most commonly used with optional arguments that

specify some sort of flag. For example:

>>> parser.parse_args(['--foo'])

Namespace(foo=42)

</pre></div>

</div>

</li>

<li><code class="docutils literal notranslate">'store_true'</code> and <code class="docutils literal notranslate">'store_false'</code> - These are special cases of

<code class="docutils literal notranslate">'store_const'</code> that respectively store the values <code class="docutils literal notranslate">True</code> and <code class="docutils literal notranslate">False</code>

with default values of <code class="docutils literal notranslate">False</code> and

<code class="docutils literal notranslate">True</code>:

>>> parser.parse_args('--foo --bar'.split())

Namespace(foo=True, bar=False, baz=True)

</pre></div>

</div>

</li>

<li><code class="docutils literal notranslate">'append'</code> - This appends each argument value to a list.

It is useful for allowing an option to be specified multiple times.

If the default value is a non-empty list, the parsed value will start

with the default list's elements and any values from the command line

will be appended after those default values. Example usage:

>>> parser.parse_args('--foo 1 --foo 2'.split())

Namespace(foo=['0', '1', '2'])

</pre></div>

</div>

</li>

<li><code class="docutils literal notranslate">'append_const'</code> - This appends the value specified by

the <a class="reference internal" href="#const">const</a> keyword argument to a list; note that the <a class="reference internal" href="#const">const</a> keyword

argument defaults to <code class="docutils literal notranslate">None</code>. The <code class="docutils literal notranslate">'append_const'</code> action is typically

useful when multiple arguments need to store constants to the same list. For

example:

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