2010-03-02 22:34:37 +00:00
|
|
|
:mod:`argparse` -- Parser for command line options, arguments and sub-commands
|
|
|
|
==============================================================================
|
|
|
|
|
|
|
|
.. module:: argparse
|
|
|
|
:synopsis: Command-line option and argument parsing library.
|
|
|
|
.. moduleauthor:: Steven Bethard <steven.bethard@gmail.com>
|
|
|
|
.. versionadded:: 2.7
|
|
|
|
.. sectionauthor:: Steven Bethard <steven.bethard@gmail.com>
|
|
|
|
|
|
|
|
|
|
|
|
The :mod:`argparse` module makes it easy to write user friendly command line
|
|
|
|
interfaces. You define what arguments your program requires, and :mod:`argparse`
|
|
|
|
will figure out how to parse those out of :data:`sys.argv`. The :mod:`argparse`
|
|
|
|
module also automatically generates help and usage messages based on the
|
|
|
|
arguments you have defined, and issues errors when users give your program
|
|
|
|
invalid arguments.
|
|
|
|
|
|
|
|
Example
|
|
|
|
-------
|
|
|
|
|
|
|
|
As an example, the following code is a Python program that takes a list of
|
|
|
|
integers and produces either the sum or the max::
|
|
|
|
|
|
|
|
import argparse
|
|
|
|
|
|
|
|
parser = argparse.ArgumentParser(description='Process some integers.')
|
|
|
|
parser.add_argument('integers', metavar='N', type=int, nargs='+',
|
|
|
|
help='an integer for the accumulator')
|
|
|
|
parser.add_argument('--sum', dest='accumulate', action='store_const',
|
|
|
|
const=sum, default=max,
|
|
|
|
help='sum the integers (default: find the max)')
|
|
|
|
|
|
|
|
args = parser.parse_args()
|
|
|
|
print args.accumulate(args.integers)
|
|
|
|
|
|
|
|
Assuming the Python code above is saved into a file called ``prog.py``, it can
|
|
|
|
be run at the command line and provides useful help messages::
|
|
|
|
|
|
|
|
$ prog.py -h
|
|
|
|
usage: prog.py [-h] [--sum] N [N ...]
|
|
|
|
|
|
|
|
Process some integers.
|
|
|
|
|
|
|
|
positional arguments:
|
|
|
|
N an integer for the accumulator
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--sum sum the integers (default: find the max)
|
|
|
|
|
|
|
|
When run with the appropriate arguments, it prints either the sum or the max of
|
|
|
|
the command-line integers::
|
|
|
|
|
|
|
|
$ prog.py 1 2 3 4
|
|
|
|
4
|
|
|
|
|
|
|
|
$ prog.py 1 2 3 4 --sum
|
|
|
|
10
|
|
|
|
|
|
|
|
If invalid arguments are passed in, it will issue an error::
|
|
|
|
|
|
|
|
$ prog.py a b c
|
|
|
|
usage: prog.py [-h] [--sum] N [N ...]
|
|
|
|
prog.py: error: argument N: invalid int value: 'a'
|
|
|
|
|
|
|
|
The following sections walk you through this example.
|
|
|
|
|
|
|
|
Creating a parser
|
|
|
|
^^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
Pretty much every script that uses the :mod:`argparse` module will start out by
|
|
|
|
creating an :class:`ArgumentParser` object::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(description='Process some integers.')
|
|
|
|
|
|
|
|
The :class:`ArgumentParser` object will hold all the information necessary to
|
|
|
|
parse the command line into a more manageable form for your program.
|
|
|
|
|
|
|
|
|
|
|
|
Adding arguments
|
|
|
|
^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
Once you've created an :class:`ArgumentParser`, you'll want to fill it with
|
|
|
|
information about your program arguments. You typically do this by making calls
|
|
|
|
to the :meth:`add_argument` method. Generally, these calls tell the
|
|
|
|
:class:`ArgumentParser` how to take the strings on the command line and turn
|
|
|
|
them into objects for you. This information is stored and used when
|
|
|
|
:meth:`parse_args` is called. For example, if we add some arguments like this::
|
|
|
|
|
|
|
|
>>> parser.add_argument('integers', metavar='N', type=int, nargs='+',
|
|
|
|
... help='an integer for the accumulator')
|
|
|
|
>>> parser.add_argument('--sum', dest='accumulate', action='store_const',
|
|
|
|
... const=sum, default=max,
|
|
|
|
... help='sum the integers (default: find the max)')
|
|
|
|
|
|
|
|
when we later call :meth:`parse_args`, we can expect it to return an object with
|
|
|
|
two attributes, ``integers`` and ``accumulate``. The ``integers`` attribute
|
|
|
|
will be a list of one or more ints, and the ``accumulate`` attribute will be
|
|
|
|
either the :func:`sum` function, if ``--sum`` was specified at the command line,
|
|
|
|
or the :func:`max` function if it was not.
|
|
|
|
|
|
|
|
Parsing arguments
|
|
|
|
^^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
Once an :class:`ArgumentParser` has been initialized with appropriate calls to
|
|
|
|
:meth:`add_argument`, it can be instructed to parse the command-line args by
|
|
|
|
calling the :meth:`parse_args` method. This will inspect the command-line,
|
|
|
|
convert each arg to the appropriate type and then invoke the appropriate action.
|
|
|
|
In most cases, this means a simple namespace object will be built up from
|
|
|
|
attributes parsed out of the command-line::
|
|
|
|
|
|
|
|
>>> parser.parse_args(['--sum', '7', '-1', '42'])
|
|
|
|
Namespace(accumulate=<built-in function sum>, integers=[7, -1, 42])
|
|
|
|
|
|
|
|
In a script, :meth:`parse_args` will typically be called with no arguments, and
|
|
|
|
the :class:`ArgumentParser` will automatically determine the command-line args
|
|
|
|
from :data:`sys.argv`. That's pretty much it. You're now ready to go write
|
|
|
|
some command line interfaces!
|
|
|
|
|
|
|
|
|
|
|
|
ArgumentParser objects
|
|
|
|
----------------------
|
|
|
|
|
|
|
|
.. class:: ArgumentParser([description], [epilog], [prog], [usage], [add_help], [argument_default], [parents], [prefix_chars], [conflict_handler], [formatter_class])
|
|
|
|
|
|
|
|
Create a new :class:`ArgumentParser` object. Each parameter has its own more
|
|
|
|
detailed description below, but in short they are:
|
|
|
|
|
|
|
|
* description_ - Text to display before the argument help.
|
|
|
|
|
|
|
|
* epilog_ - Text to display after the argument help.
|
|
|
|
|
|
|
|
* add_help_ - Add a -h/--help option to the parser. (default: True)
|
|
|
|
|
|
|
|
* argument_default_ - Set the global default value for arguments.
|
|
|
|
(default: None)
|
|
|
|
|
|
|
|
* parents_ - A list of :class:ArgumentParser objects whose arguments should
|
|
|
|
also be included.
|
|
|
|
|
|
|
|
* prefix_chars_ - The set of characters that prefix optional arguments.
|
|
|
|
(default: '-')
|
|
|
|
|
|
|
|
* fromfile_prefix_chars_ - The set of characters that prefix files from
|
|
|
|
which additional arguments should be read. (default: None)
|
|
|
|
|
|
|
|
* formatter_class_ - A class for customizing the help output.
|
|
|
|
|
|
|
|
* conflict_handler_ - Usually unnecessary, defines strategy for resolving
|
|
|
|
conflicting optionals.
|
|
|
|
|
|
|
|
* prog_ - Usually unnecessary, the name of the program
|
|
|
|
(default: ``sys.argv[0]``)
|
|
|
|
|
|
|
|
* usage_ - Usually unnecessary, the string describing the program usage
|
|
|
|
(default: generated)
|
|
|
|
|
|
|
|
The following sections describe how each of these are used.
|
|
|
|
|
|
|
|
|
|
|
|
description
|
|
|
|
^^^^^^^^^^^
|
|
|
|
|
|
|
|
Most calls to the ArgumentParser constructor will use the ``description=``
|
|
|
|
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::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(description='A foo that bars')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: argparse.py [-h]
|
|
|
|
|
|
|
|
A foo that bars
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
|
|
|
|
By default, the description will be line-wrapped so that it fits within the
|
|
|
|
given space. To change this behavior, see the formatter_class_ argument.
|
|
|
|
|
|
|
|
|
|
|
|
epilog
|
|
|
|
^^^^^^
|
|
|
|
|
|
|
|
Some programs like to display additional description of the program after the
|
|
|
|
description of the arguments. Such text can be specified using the ``epilog=``
|
|
|
|
argument to :class:`ArgumentParser`::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(
|
|
|
|
... 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
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
|
|
|
|
And that's how you'd foo a bar
|
|
|
|
|
|
|
|
As with the description_ argument, the ``epilog=`` text is by default
|
|
|
|
line-wrapped, but this behavior can be adjusted with the formatter_class_
|
|
|
|
argument to ArgumentParser.
|
|
|
|
|
|
|
|
|
|
|
|
add_help
|
|
|
|
^^^^^^^^
|
|
|
|
|
|
|
|
By default, ArgumentParser objects add a ``-h/--help`` option which simply
|
|
|
|
displays the parser's help message. For example, consider a file named
|
|
|
|
``myprogram.py`` containing the following code::
|
|
|
|
|
|
|
|
import argparse
|
|
|
|
parser = argparse.ArgumentParser()
|
|
|
|
parser.add_argument('--foo', help='foo help')
|
|
|
|
args = parser.parse_args()
|
|
|
|
|
|
|
|
If ``-h`` or ``--help`` is supplied is at the command-line, the ArgumentParser
|
|
|
|
help will be printed::
|
|
|
|
|
|
|
|
$ python myprogram.py --help
|
|
|
|
usage: myprogram.py [-h] [--foo FOO]
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo FOO foo help
|
|
|
|
|
|
|
|
Occasionally, it may be useful to disable the addition of this help option.
|
|
|
|
This can be achieved by passing ``False`` as the ``add_help=`` argument to
|
|
|
|
ArgumentParser::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG', add_help=False)
|
|
|
|
>>> parser.add_argument('--foo', help='foo help')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: PROG [--foo FOO]
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
--foo FOO foo help
|
|
|
|
|
|
|
|
|
|
|
|
prefix_chars
|
|
|
|
^^^^^^^^^^^^
|
|
|
|
|
|
|
|
Most command-line options will use ``'-'`` as the prefix, e.g. ``-f/--foo``.
|
|
|
|
Parsers that need to support additional prefix characters, e.g. for options
|
|
|
|
like ``+f`` or ``/foo``, may specify them using the ``prefix_chars=`` argument
|
|
|
|
to the ArgumentParser constructor::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG', prefix_chars='-+')
|
|
|
|
>>> parser.add_argument('+f')
|
|
|
|
>>> parser.add_argument('++bar')
|
|
|
|
>>> parser.parse_args('+f X ++bar Y'.split())
|
|
|
|
Namespace(bar='Y', f='X')
|
|
|
|
|
|
|
|
The ``prefix_chars=`` argument defaults to ``'-'``. Supplying a set of
|
|
|
|
characters that does not include ``'-'`` will cause ``-f/--foo`` options to be
|
|
|
|
disallowed.
|
|
|
|
|
|
|
|
|
|
|
|
fromfile_prefix_chars
|
|
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
Sometimes, e.g. for particularly long argument lists, it may make sense to keep
|
|
|
|
the list of arguments in a file rather than typing it out at the command line.
|
|
|
|
If the ``fromfile_prefix_chars=`` argument is given to the ArgumentParser
|
|
|
|
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::
|
|
|
|
|
|
|
|
>>> open('args.txt', 'w').write('-f\nbar')
|
|
|
|
>>> parser = argparse.ArgumentParser(fromfile_prefix_chars='@')
|
|
|
|
>>> parser.add_argument('-f')
|
|
|
|
>>> parser.parse_args(['-f', 'foo', '@args.txt'])
|
|
|
|
Namespace(f='bar')
|
|
|
|
|
|
|
|
Arguments read from a file must by default be one per line (but see also
|
|
|
|
:meth:`convert_arg_line_to_args`) 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 ``['-f', 'foo', '@args.txt']`` is considered
|
|
|
|
equivalent to the expression ``['-f', 'foo', '-f', 'bar']``.
|
|
|
|
|
|
|
|
The ``fromfile_prefix_chars=`` argument defaults to ``None``, meaning that
|
|
|
|
arguments will never be treated as file references.
|
|
|
|
|
|
|
|
argument_default
|
|
|
|
^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
Generally, argument defaults are specified either by passing a default to
|
|
|
|
:meth:`add_argument` or by calling the :meth:`set_defaults` 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 ``argument_default=`` keyword argument to ArgumentParser. For
|
|
|
|
example, to globally suppress attribute creation on :meth:`parse_args` calls, we
|
|
|
|
supply ``argument_default=SUPPRESS``::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(argument_default=argparse.SUPPRESS)
|
|
|
|
>>> parser.add_argument('--foo')
|
|
|
|
>>> parser.add_argument('bar', nargs='?')
|
|
|
|
>>> parser.parse_args(['--foo', '1', 'BAR'])
|
|
|
|
Namespace(bar='BAR', foo='1')
|
|
|
|
>>> parser.parse_args([])
|
|
|
|
Namespace()
|
|
|
|
|
|
|
|
|
|
|
|
parents
|
|
|
|
^^^^^^^
|
|
|
|
|
|
|
|
Sometimes, several parsers share a common set of arguments. Rather than
|
|
|
|
repeating the definitions of these arguments, you can define a single parser
|
|
|
|
with all the shared arguments and then use the ``parents=`` argument to
|
|
|
|
ArgumentParser to have these "inherited". The ``parents=`` argument takes a
|
|
|
|
list of ArgumentParser objects, collects all the positional and optional actions
|
|
|
|
from them, and adds these actions to the ArgumentParser object being
|
|
|
|
constructed::
|
|
|
|
|
|
|
|
>>> 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)
|
|
|
|
|
|
|
|
Note that most parent parsers will specify ``add_help=False``. Otherwise, the
|
|
|
|
ArgumentParser will see two ``-h/--help`` options (one in the parent and one in
|
|
|
|
the child) and raise an error.
|
|
|
|
|
|
|
|
|
|
|
|
formatter_class
|
|
|
|
^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
ArgumentParser objects allow the help formatting to be customized by specifying
|
|
|
|
an alternate formatting class. Currently, there are three such classes:
|
|
|
|
:class:`argparse.RawDescriptionHelpFormatter`,
|
|
|
|
:class:`argparse.RawTextHelpFormatter` and
|
|
|
|
:class:`argparse.ArgumentDefaultsHelpFormatter`. The first two allow more
|
|
|
|
control over how textual descriptions are displayed, while the last
|
|
|
|
automatically adds information about argument default values.
|
|
|
|
|
|
|
|
By default, ArgumentParser objects line-wrap the description_ and epilog_ texts
|
|
|
|
in command-line help messages::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(
|
|
|
|
... 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
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-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
|
|
|
|
|
|
|
|
When you have description_ and epilog_ that is already correctly formatted and
|
|
|
|
should not be line-wrapped, you can indicate this by passing
|
|
|
|
``argparse.RawDescriptionHelpFormatter`` as the ``formatter_class=`` argument to
|
|
|
|
ArgumentParser::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(
|
|
|
|
... 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
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
|
|
|
|
If you want to maintain whitespace for all sorts of help text (including
|
|
|
|
argument descriptions), you can use ``argparse.RawTextHelpFormatter``.
|
|
|
|
|
|
|
|
The other formatter class available, ``argparse.ArgumentDefaultsHelpFormatter``,
|
|
|
|
will add information about the default value of each of the arguments::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(
|
|
|
|
... 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 [bar ...]]
|
|
|
|
|
|
|
|
positional arguments:
|
|
|
|
bar BAR! (default: [1, 2, 3])
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo FOO FOO! (default: 42)
|
|
|
|
|
|
|
|
|
|
|
|
conflict_handler
|
|
|
|
^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
ArgumentParser objects do not allow two actions with the same option string. By
|
|
|
|
default, ArgumentParser objects will raise an exception if you try to create an
|
|
|
|
argument with an option string that is already in use::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('-f', '--foo', help='old foo help')
|
|
|
|
>>> parser.add_argument('--foo', help='new foo help')
|
|
|
|
Traceback (most recent call last):
|
|
|
|
..
|
|
|
|
ArgumentError: argument --foo: conflicting option string(s): --foo
|
|
|
|
|
|
|
|
Sometimes (e.g. when using parents_) it may be useful to simply override any
|
|
|
|
older arguments with the same option string. To get this behavior, the value
|
|
|
|
``'resolve'`` can be supplied to the ``conflict_handler=`` argument of
|
|
|
|
ArgumentParser::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG', conflict_handler='resolve')
|
|
|
|
>>> parser.add_argument('-f', '--foo', help='old foo help')
|
|
|
|
>>> parser.add_argument('--foo', help='new foo help')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: PROG [-h] [-f FOO] [--foo FOO]
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
-f FOO old foo help
|
|
|
|
--foo FOO new foo help
|
|
|
|
|
|
|
|
Note that ArgumentParser objects only remove an action if all of its option
|
|
|
|
strings are overridden. So, in the example above, the old ``-f/--foo`` action
|
|
|
|
is retained as the ``-f`` action, because only the ``--foo`` option string was
|
|
|
|
overridden.
|
|
|
|
|
|
|
|
|
|
|
|
prog
|
|
|
|
^^^^
|
|
|
|
|
|
|
|
By default, ArgumentParser objects use ``sys.argv[0]`` to determine how to
|
|
|
|
display the name of the program in help messages. This default is almost always
|
|
|
|
what you want because it will make the help messages match what your users have
|
|
|
|
typed at the command line. For example, consider a file named ``myprogram.py``
|
|
|
|
with the following code::
|
|
|
|
|
|
|
|
import argparse
|
|
|
|
parser = argparse.ArgumentParser()
|
|
|
|
parser.add_argument('--foo', help='foo help')
|
|
|
|
args = parser.parse_args()
|
|
|
|
|
|
|
|
The help for this program will display ``myprogram.py`` as the program name
|
|
|
|
(regardless of where the program was invoked from)::
|
|
|
|
|
|
|
|
$ python myprogram.py --help
|
|
|
|
usage: myprogram.py [-h] [--foo FOO]
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo FOO foo help
|
|
|
|
$ cd ..
|
|
|
|
$ python subdir\myprogram.py --help
|
|
|
|
usage: myprogram.py [-h] [--foo FOO]
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo FOO foo help
|
|
|
|
|
|
|
|
To change this default behavior, another value can be supplied using the
|
|
|
|
``prog=`` argument to ArgumentParser::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='myprogram')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: myprogram [-h]
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
|
|
|
|
Note that the program name, whether determined from ``sys.argv[0]`` or from the
|
|
|
|
``prog=`` argument, is available to help messages using the ``%(prog)s`` format
|
|
|
|
specifier.
|
|
|
|
|
|
|
|
::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='myprogram')
|
|
|
|
>>> parser.add_argument('--foo', help='foo of the %(prog)s program')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: myprogram [-h] [--foo FOO]
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo FOO foo of the myprogram program
|
|
|
|
|
|
|
|
|
|
|
|
usage
|
|
|
|
^^^^^
|
|
|
|
|
|
|
|
By default, ArgumentParser objects calculate the usage message from the
|
|
|
|
arguments it contains::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('--foo', nargs='?', help='foo help')
|
|
|
|
>>> parser.add_argument('bar', nargs='+', help='bar help')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: PROG [-h] [--foo [FOO]] bar [bar ...]
|
|
|
|
|
|
|
|
positional arguments:
|
|
|
|
bar bar help
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo [FOO] foo help
|
|
|
|
|
|
|
|
If the default usage message is not appropriate for your application, you can
|
|
|
|
supply your own usage message using the ``usage=`` keyword argument to
|
|
|
|
ArgumentParser::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG', usage='%(prog)s [options]')
|
|
|
|
>>> parser.add_argument('--foo', nargs='?', help='foo help')
|
|
|
|
>>> parser.add_argument('bar', nargs='+', help='bar help')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: PROG [options]
|
|
|
|
|
|
|
|
positional arguments:
|
|
|
|
bar bar help
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo [FOO] foo help
|
|
|
|
|
|
|
|
Note you can use the ``%(prog)s`` format specifier to fill in the program name
|
|
|
|
in your usage messages.
|
|
|
|
|
|
|
|
|
|
|
|
The add_argument() method
|
|
|
|
-------------------------
|
|
|
|
|
|
|
|
.. method:: add_argument(name or flags..., [action], [nargs], [const], [default], [type], [choices], [required], [help], [metavar], [dest])
|
|
|
|
|
|
|
|
Define how a single command line argument should be parsed. Each parameter
|
|
|
|
has its own more detailed description below, but in short they are:
|
|
|
|
|
|
|
|
* `name or flags`_ - Either a name or a list of option strings, e.g. ``foo``
|
|
|
|
or ``-f, --foo``
|
|
|
|
|
|
|
|
* action_ - The basic type of action to be taken when this argument is
|
|
|
|
encountered at the command-line.
|
|
|
|
|
|
|
|
* nargs_ - The number of command-line arguments that should be consumed.
|
|
|
|
|
|
|
|
* const_ - A constant value required by some action_ and nargs_ selections.
|
|
|
|
|
|
|
|
* default_ - The value produced if the argument is absent from the
|
|
|
|
command-line.
|
|
|
|
|
|
|
|
* type_ - The type to which the command-line arg should be converted.
|
|
|
|
|
|
|
|
* choices_ - A container of the allowable values for the argument.
|
|
|
|
|
|
|
|
* required_ - Whether or not the command-line option may be omitted
|
|
|
|
(optionals only).
|
|
|
|
|
|
|
|
* help_ - A brief description of what the argument does.
|
|
|
|
|
|
|
|
* metavar_ - A name for the argument in usage messages.
|
|
|
|
|
|
|
|
* dest_ - The name of the attribute to be added to the object returned by
|
|
|
|
:meth:`parse_args`.
|
|
|
|
|
|
|
|
The following sections describe how each of these are used.
|
|
|
|
|
|
|
|
name or flags
|
|
|
|
^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
The :meth:`add_argument` method needs to know whether you're expecting an
|
|
|
|
optional argument, e.g. ``-f`` or ``--foo``, or a positional argument, e.g. a
|
|
|
|
list of filenames. The first arguments passed to :meth:`add_argument` must
|
|
|
|
therefore be either a series of flags, or a simple argument name. For example,
|
|
|
|
an optional argument could be created like::
|
|
|
|
|
|
|
|
>>> parser.add_argument('-f', '--foo')
|
|
|
|
|
|
|
|
while a positional argument could be created like::
|
|
|
|
|
|
|
|
>>> parser.add_argument('bar')
|
|
|
|
|
|
|
|
When :meth:`parse_args` is called, optional arguments will be identified by the
|
|
|
|
``-`` prefix, and the remaining arguments will be assumed to be positional::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('-f', '--foo')
|
|
|
|
>>> 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: too few arguments
|
|
|
|
|
|
|
|
action
|
|
|
|
^^^^^^
|
|
|
|
|
|
|
|
:class:`ArgumentParser` objects associate command-line args with actions. These
|
|
|
|
actions can do just about anything with the command-line args associated with
|
|
|
|
them, though most actions simply add an attribute to the object returned by
|
|
|
|
:meth:`parse_args`. When you specify a new argument using the
|
|
|
|
:meth:`add_argument` method, you can indicate how the command-line args should
|
|
|
|
be handled by specifying the ``action`` keyword argument. The supported actions
|
|
|
|
are:
|
|
|
|
|
|
|
|
* ``'store'`` - This just stores the argument's value. This is the default
|
|
|
|
action. For example::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo')
|
|
|
|
>>> parser.parse_args('--foo 1'.split())
|
|
|
|
Namespace(foo='1')
|
|
|
|
|
|
|
|
* ``'store_const'`` - This stores the value specified by the const_ keyword
|
|
|
|
argument. Note that the const_ keyword argument defaults to ``None``, so
|
|
|
|
you'll almost always need to provide a value for it. The ``'store_const'``
|
|
|
|
action is most commonly used with optional arguments that specify some sort
|
|
|
|
of flag. For example::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', action='store_const', const=42)
|
|
|
|
>>> parser.parse_args('--foo'.split())
|
|
|
|
Namespace(foo=42)
|
|
|
|
|
|
|
|
* ``'store_true'`` and ``'store_false'`` - These store the values ``True`` and
|
|
|
|
``False`` respectively. These are basically special cases of
|
|
|
|
``'store_const'``. For example::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', action='store_true')
|
|
|
|
>>> parser.add_argument('--bar', action='store_false')
|
|
|
|
>>> parser.parse_args('--foo --bar'.split())
|
|
|
|
Namespace(bar=False, foo=True)
|
|
|
|
|
|
|
|
* ``'append'`` - This stores a list, and appends each argument value to the
|
|
|
|
list. This is useful when you want to allow an option to be specified
|
|
|
|
multiple times. Example usage::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', action='append')
|
|
|
|
>>> parser.parse_args('--foo 1 --foo 2'.split())
|
|
|
|
Namespace(foo=['1', '2'])
|
|
|
|
|
|
|
|
* ``'append_const'`` - This stores a list, and appends the value specified by
|
|
|
|
the const_ keyword argument to the list. Note that the const_ keyword
|
|
|
|
argument defaults to ``None``, so you'll almost always need to provide a value
|
|
|
|
for it. The ``'append_const'`` action is typically useful when you want
|
|
|
|
multiple arguments to store constants to the same list, for example::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--str', dest='types', action='append_const', const=str)
|
|
|
|
>>> parser.add_argument('--int', dest='types', action='append_const', const=int)
|
|
|
|
>>> parser.parse_args('--str --int'.split())
|
|
|
|
Namespace(types=[<type 'str'>, <type 'int'>])
|
|
|
|
|
|
|
|
* ``'version'`` - This expects a ``version=`` keyword argument in the
|
|
|
|
:meth:`add_argument` call, and prints version information and exits when
|
|
|
|
invoked.
|
|
|
|
|
|
|
|
>>> import argparse
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('-v', '--version', action='version', version='%(prog)s 2.0')
|
|
|
|
>>> parser.parse_args(['-v'])
|
|
|
|
PROG 2.0
|
|
|
|
|
|
|
|
You can also specify an arbitrary action by passing an object that implements
|
|
|
|
the Action API. The easiest way to do this is to extend ``argparse.Action``,
|
|
|
|
supplying an appropriate :meth:`__call__` method. The ``__call__`` method
|
|
|
|
accepts four parameters:
|
|
|
|
|
|
|
|
* ``parser`` - The ArgumentParser object which contains this action.
|
|
|
|
|
|
|
|
* ``namespace`` - The namespace object that will be returned by
|
|
|
|
:meth:`parse_args`. Most actions add an attribute to this object.
|
|
|
|
|
|
|
|
* ``values`` - The associated command-line args, with any type-conversions
|
|
|
|
applied. (Type-conversions are specified with the type_ keyword argument to
|
|
|
|
:meth:`add_argument`.
|
|
|
|
|
|
|
|
* ``option_string`` - The option string that was used to invoke this action.
|
|
|
|
The ``option_string`` argument is optional, and will be absent if the action
|
|
|
|
is associated with a positional argument.
|
|
|
|
|
|
|
|
So for example::
|
|
|
|
|
|
|
|
>>> class FooAction(argparse.Action):
|
|
|
|
... def __call__(self, parser, namespace, values, option_string=None):
|
|
|
|
... print '%r %r %r' % (namespace, values, option_string)
|
|
|
|
... setattr(namespace, self.dest, values)
|
|
|
|
...
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', action=FooAction)
|
|
|
|
>>> parser.add_argument('bar', action=FooAction)
|
|
|
|
>>> args = parser.parse_args('1 --foo 2'.split())
|
|
|
|
Namespace(bar=None, foo=None) '1' None
|
|
|
|
Namespace(bar='1', foo=None) '2' '--foo'
|
|
|
|
>>> args
|
|
|
|
Namespace(bar='1', foo='2')
|
|
|
|
|
|
|
|
|
|
|
|
nargs
|
|
|
|
^^^^^
|
|
|
|
|
|
|
|
ArgumentParser objects usually associate a single command-line argument with a
|
|
|
|
single action to be taken. In the situations where you'd like to associate a
|
|
|
|
different number of command-line arguments with a single action, you can use the
|
|
|
|
``nargs`` keyword argument to :meth:`add_argument`. The supported values are:
|
|
|
|
|
|
|
|
* N (an integer). N args from the command-line will be gathered together into a
|
|
|
|
list. For example::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', nargs=2)
|
|
|
|
>>> parser.add_argument('bar', nargs=1)
|
|
|
|
>>> parser.parse_args('c --foo a b'.split())
|
|
|
|
Namespace(bar=['c'], foo=['a', 'b'])
|
|
|
|
|
|
|
|
Note that ``nargs=1`` produces a list of one item. This is different from
|
|
|
|
the default, in which the item is produced by itself.
|
|
|
|
|
|
|
|
* ``'?'``. One arg will be consumed from the command-line if possible, and
|
|
|
|
produced as a single item. If no command-line arg is present, the value from
|
|
|
|
default_ will be produced. Note that for optional arguments, there is an
|
|
|
|
additional case - the option string is present but not followed by a
|
|
|
|
command-line arg. In this case the value from const_ will be produced. Some
|
|
|
|
examples to illustrate this::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', nargs='?', const='c', default='d')
|
|
|
|
>>> parser.add_argument('bar', nargs='?', default='d')
|
|
|
|
>>> parser.parse_args('XX --foo YY'.split())
|
|
|
|
Namespace(bar='XX', foo='YY')
|
|
|
|
>>> parser.parse_args('XX --foo'.split())
|
|
|
|
Namespace(bar='XX', foo='c')
|
|
|
|
>>> parser.parse_args(''.split())
|
|
|
|
Namespace(bar='d', foo='d')
|
|
|
|
|
|
|
|
One of the more common uses of ``nargs='?'`` is to allow optional input and
|
|
|
|
output files::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('infile', nargs='?', type=argparse.FileType('r'), default=sys.stdin)
|
|
|
|
>>> parser.add_argument('outfile', nargs='?', type=argparse.FileType('w'), default=sys.stdout)
|
|
|
|
>>> parser.parse_args(['input.txt', 'output.txt'])
|
|
|
|
Namespace(infile=<open file 'input.txt', mode 'r' at 0x...>, outfile=<open file 'output.txt', mode 'w' at 0x...>)
|
|
|
|
>>> parser.parse_args([])
|
|
|
|
Namespace(infile=<open file '<stdin>', mode 'r' at 0x...>, outfile=<open file '<stdout>', mode 'w' at 0x...>)
|
|
|
|
|
|
|
|
* ``'*'``. All command-line args present are gathered into a list. Note that
|
|
|
|
it generally doesn't make much sense to have more than one positional argument
|
|
|
|
with ``nargs='*'``, but multiple optional arguments with ``nargs='*'`` is
|
|
|
|
possible. For example::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', nargs='*')
|
|
|
|
>>> parser.add_argument('--bar', nargs='*')
|
|
|
|
>>> parser.add_argument('baz', nargs='*')
|
|
|
|
>>> parser.parse_args('a b --foo x y --bar 1 2'.split())
|
|
|
|
Namespace(bar=['1', '2'], baz=['a', 'b'], foo=['x', 'y'])
|
|
|
|
|
|
|
|
* ``'+'``. Just like ``'*'``, all command-line args present are gathered into a
|
|
|
|
list. Additionally, an error message will be generated if there wasn't at
|
|
|
|
least one command-line arg present. For example::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('foo', nargs='+')
|
|
|
|
>>> parser.parse_args('a b'.split())
|
|
|
|
Namespace(foo=['a', 'b'])
|
|
|
|
>>> parser.parse_args(''.split())
|
|
|
|
usage: PROG [-h] foo [foo ...]
|
|
|
|
PROG: error: too few arguments
|
|
|
|
|
|
|
|
If the ``nargs`` keyword argument is not provided, the number of args consumed
|
|
|
|
is determined by the action_. Generally this means a single command-line arg
|
|
|
|
will be consumed and a single item (not a list) will be produced.
|
|
|
|
|
|
|
|
|
|
|
|
const
|
|
|
|
^^^^^
|
|
|
|
|
|
|
|
The ``const`` argument of :meth:`add_argument` is used to hold constant values
|
|
|
|
that are not read from the command line but are required for the various
|
|
|
|
ArgumentParser actions. The two most common uses of it are:
|
|
|
|
|
|
|
|
* When :meth:`add_argument` is called with ``action='store_const'`` or
|
|
|
|
``action='append_const'``. These actions add the ``const`` value to one of
|
|
|
|
the attributes of the object returned by :meth:`parse_args`. See the action_
|
|
|
|
description for examples.
|
|
|
|
|
|
|
|
* When :meth:`add_argument` is called with option strings (like ``-f`` or
|
|
|
|
``--foo``) and ``nargs='?'``. This creates an optional argument that can be
|
|
|
|
followed by zero or one command-line args. When parsing the command-line, if
|
|
|
|
the option string is encountered with no command-line arg following it, the
|
|
|
|
value of ``const`` will be assumed instead. See the nargs_ description for
|
|
|
|
examples.
|
|
|
|
|
|
|
|
The ``const`` keyword argument defaults to ``None``.
|
|
|
|
|
|
|
|
|
|
|
|
default
|
|
|
|
^^^^^^^
|
|
|
|
|
|
|
|
All optional arguments and some positional arguments may be omitted at the
|
|
|
|
command-line. The ``default`` keyword argument of :meth:`add_argument`, whose
|
|
|
|
value defaults to ``None``, specifies what value should be used if the
|
|
|
|
command-line arg is not present. For optional arguments, the ``default`` value
|
|
|
|
is used when the option string was not present at the command line::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', default=42)
|
|
|
|
>>> parser.parse_args('--foo 2'.split())
|
|
|
|
Namespace(foo='2')
|
|
|
|
>>> parser.parse_args(''.split())
|
|
|
|
Namespace(foo=42)
|
|
|
|
|
|
|
|
For positional arguments with nargs_ ``='?'`` or ``'*'``, the ``default`` value
|
|
|
|
is used when no command-line arg was present::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('foo', nargs='?', default=42)
|
|
|
|
>>> parser.parse_args('a'.split())
|
|
|
|
Namespace(foo='a')
|
|
|
|
>>> parser.parse_args(''.split())
|
|
|
|
Namespace(foo=42)
|
|
|
|
|
|
|
|
|
|
|
|
If you don't want to see an attribute when an option was not present at the
|
|
|
|
command line, you can supply ``default=argparse.SUPPRESS``::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', default=argparse.SUPPRESS)
|
|
|
|
>>> parser.parse_args([])
|
|
|
|
Namespace()
|
|
|
|
>>> parser.parse_args(['--foo', '1'])
|
|
|
|
Namespace(foo='1')
|
|
|
|
|
|
|
|
|
|
|
|
type
|
|
|
|
^^^^
|
|
|
|
|
|
|
|
By default, ArgumentParser objects read command-line args in as simple strings.
|
|
|
|
However, quite often the command-line string should instead be interpreted as
|
|
|
|
another type, e.g. :class:`float`, :class:`int` or :class:`file`. The ``type``
|
|
|
|
keyword argument of :meth:`add_argument` allows any necessary type-checking and
|
|
|
|
type-conversions to be performed. Many common builtin types can be used
|
|
|
|
directly as the value of the ``type`` argument::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('foo', type=int)
|
|
|
|
>>> parser.add_argument('bar', type=file)
|
|
|
|
>>> parser.parse_args('2 temp.txt'.split())
|
|
|
|
Namespace(bar=<open file 'temp.txt', mode 'r' at 0x...>, foo=2)
|
|
|
|
|
|
|
|
To ease the use of various types of files, the argparse module provides the
|
|
|
|
factory FileType which takes the ``mode=`` and ``bufsize=`` arguments of the
|
|
|
|
``file`` object. For example, ``FileType('w')`` can be used to create a
|
|
|
|
writable file::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('bar', type=argparse.FileType('w'))
|
|
|
|
>>> parser.parse_args(['out.txt'])
|
|
|
|
Namespace(bar=<open file 'out.txt', mode 'w' at 0x...>)
|
|
|
|
|
|
|
|
If you need to do some special type-checking or type-conversions, you can
|
|
|
|
provide your own types by passing to ``type=`` a callable that takes a single
|
|
|
|
string argument and returns the type-converted value::
|
|
|
|
|
|
|
|
>>> def perfect_square(string):
|
|
|
|
... value = int(string)
|
|
|
|
... sqrt = math.sqrt(value)
|
|
|
|
... if sqrt != int(sqrt):
|
|
|
|
... msg = "%r is not a perfect square" % string
|
|
|
|
... raise argparse.ArgumentTypeError(msg)
|
|
|
|
... return value
|
|
|
|
...
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('foo', type=perfect_square)
|
|
|
|
>>> parser.parse_args('9'.split())
|
|
|
|
Namespace(foo=9)
|
|
|
|
>>> parser.parse_args('7'.split())
|
|
|
|
usage: PROG [-h] foo
|
|
|
|
PROG: error: argument foo: '7' is not a perfect square
|
|
|
|
|
|
|
|
Note that if your type-checking function is just checking for a particular set
|
|
|
|
of values, it may be more convenient to use the choices_ keyword argument::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('foo', type=int, choices=xrange(5, 10))
|
|
|
|
>>> parser.parse_args('7'.split())
|
|
|
|
Namespace(foo=7)
|
|
|
|
>>> parser.parse_args('11'.split())
|
|
|
|
usage: PROG [-h] {5,6,7,8,9}
|
|
|
|
PROG: error: argument foo: invalid choice: 11 (choose from 5, 6, 7, 8, 9)
|
|
|
|
|
|
|
|
See the choices_ section for more details.
|
|
|
|
|
|
|
|
|
|
|
|
choices
|
|
|
|
^^^^^^^
|
|
|
|
|
|
|
|
Some command-line args should be selected from a restricted set of values.
|
|
|
|
ArgumentParser objects can be told about such sets of values by passing a
|
|
|
|
container object as the ``choices`` keyword argument to :meth:`add_argument`.
|
|
|
|
When the command-line is parsed with :meth:`parse_args`, arg values will be
|
|
|
|
checked, and an error message will be displayed if the arg was not one of the
|
|
|
|
acceptable values::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('foo', choices='abc')
|
|
|
|
>>> parser.parse_args('c'.split())
|
|
|
|
Namespace(foo='c')
|
|
|
|
>>> parser.parse_args('X'.split())
|
|
|
|
usage: PROG [-h] {a,b,c}
|
|
|
|
PROG: error: argument foo: invalid choice: 'X' (choose from 'a', 'b', 'c')
|
|
|
|
|
|
|
|
Note that inclusion in the ``choices`` container is checked after any type_
|
|
|
|
conversions have been performed, so the type of the objects in the ``choices``
|
|
|
|
container should match the type_ specified::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('foo', type=complex, choices=[1, 1j])
|
|
|
|
>>> parser.parse_args('1j'.split())
|
|
|
|
Namespace(foo=1j)
|
|
|
|
>>> parser.parse_args('-- -4'.split())
|
|
|
|
usage: PROG [-h] {1,1j}
|
|
|
|
PROG: error: argument foo: invalid choice: (-4+0j) (choose from 1, 1j)
|
|
|
|
|
|
|
|
Any object that supports the ``in`` operator can be passed as the ``choices``
|
|
|
|
value, so :class:`dict` objects, :class:`set` objects, custom containers,
|
|
|
|
etc. are all supported.
|
|
|
|
|
|
|
|
|
|
|
|
required
|
|
|
|
^^^^^^^^
|
|
|
|
|
|
|
|
In general, the argparse module assumes that flags like ``-f`` and ``--bar``
|
|
|
|
indicate *optional* arguments, which can always be omitted at the command-line.
|
|
|
|
To change this behavior, i.e. to make an option *required*, the value ``True``
|
|
|
|
should be specified for the ``required=`` keyword argument to
|
|
|
|
:meth:`add_argument`::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', required=True)
|
|
|
|
>>> parser.parse_args(['--foo', 'BAR'])
|
|
|
|
Namespace(foo='BAR')
|
|
|
|
>>> parser.parse_args([])
|
|
|
|
usage: argparse.py [-h] [--foo FOO]
|
|
|
|
argparse.py: error: option --foo is required
|
|
|
|
|
|
|
|
As the example shows, if an option is marked as ``required``, :meth:`parse_args`
|
|
|
|
will report an error if that option is not present at the command line.
|
|
|
|
|
|
|
|
**Warning:** Required options are generally considered bad form - normal users
|
|
|
|
expect *options* to be *optional*. You should avoid the use of required options
|
|
|
|
whenever possible.
|
|
|
|
|
|
|
|
|
|
|
|
help
|
|
|
|
^^^^
|
|
|
|
|
|
|
|
A great command-line interface isn't worth anything if your users can't figure
|
|
|
|
out which option does what. So for the end-users, ``help`` is probably the most
|
|
|
|
important argument to include in your :meth:`add_argument` calls. The ``help``
|
|
|
|
value should be a string containing a brief description of what the argument
|
|
|
|
specifies. When a user requests help (usually by using ``-h`` or ``--help`` at
|
|
|
|
the command-line), these ``help`` descriptions will be displayed with each
|
|
|
|
argument::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='frobble')
|
|
|
|
>>> parser.add_argument('--foo', action='store_true',
|
|
|
|
... help='foo the bars before frobbling')
|
|
|
|
>>> parser.add_argument('bar', nargs='+',
|
|
|
|
... help='one of the bars to be frobbled')
|
|
|
|
>>> parser.parse_args('-h'.split())
|
|
|
|
usage: frobble [-h] [--foo] bar [bar ...]
|
|
|
|
|
|
|
|
positional arguments:
|
|
|
|
bar one of the bars to be frobbled
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo foo the bars before frobbling
|
|
|
|
|
|
|
|
The ``help`` strings can include various format specifiers to avoid repetition
|
|
|
|
of things like the program name or the argument default_. The available
|
|
|
|
specifiers include the program name, ``%(prog)s`` and most keyword arguments to
|
|
|
|
:meth:`add_argument`, e.g. ``%(default)s``, ``%(type)s``, etc.::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='frobble')
|
|
|
|
>>> parser.add_argument('bar', nargs='?', type=int, default=42,
|
|
|
|
... help='the bar to %(prog)s (default: %(default)s)')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: frobble [-h] [bar]
|
|
|
|
|
|
|
|
positional arguments:
|
|
|
|
bar the bar to frobble (default: 42)
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
|
|
|
|
|
|
|
|
metavar
|
|
|
|
^^^^^^^
|
|
|
|
|
|
|
|
When ArgumentParser objects generate help messages, they need some way to refer
|
|
|
|
to each expected argument. By default, ArgumentParser objects use the dest_
|
|
|
|
value as the "name" of each object. By default, for positional argument
|
|
|
|
actions, the dest_ value is used directly, and for optional argument actions,
|
|
|
|
the dest_ value is uppercased. So if we have a single positional argument with
|
|
|
|
``dest='bar'``, that argument will be referred to as ``bar``. And if we have a
|
|
|
|
single optional argument ``--foo`` that should be followed by a single
|
|
|
|
command-line arg, that arg will be referred to as ``FOO``. You can see this
|
|
|
|
behavior in the example below::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo')
|
|
|
|
>>> parser.add_argument('bar')
|
|
|
|
>>> parser.parse_args('X --foo Y'.split())
|
|
|
|
Namespace(bar='X', foo='Y')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: [-h] [--foo FOO] bar
|
|
|
|
|
|
|
|
positional arguments:
|
|
|
|
bar
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo FOO
|
|
|
|
|
|
|
|
If you would like to provide a different name for your argument in help
|
|
|
|
messages, you can supply a value for the ``metavar`` keyword argument to
|
|
|
|
:meth:`add_argument`::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', metavar='YYY')
|
|
|
|
>>> parser.add_argument('bar', metavar='XXX')
|
|
|
|
>>> parser.parse_args('X --foo Y'.split())
|
|
|
|
Namespace(bar='X', foo='Y')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: [-h] [--foo YYY] XXX
|
|
|
|
|
|
|
|
positional arguments:
|
|
|
|
XXX
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo YYY
|
|
|
|
|
|
|
|
Note that ``metavar`` only changes the *displayed* name - the name of the
|
|
|
|
attribute on the :meth:`parse_args` object is still determined by the dest_
|
|
|
|
value.
|
|
|
|
|
|
|
|
Different values of ``nargs`` may cause the metavar to be used multiple times.
|
|
|
|
If you'd like to specify a different display name for each of the arguments, you
|
|
|
|
can provide a tuple to ``metavar``::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('-x', nargs=2)
|
|
|
|
>>> parser.add_argument('--foo', nargs=2, metavar=('bar', 'baz'))
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: PROG [-h] [-x X X] [--foo bar baz]
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
-x X X
|
|
|
|
--foo bar baz
|
|
|
|
|
|
|
|
|
|
|
|
dest
|
|
|
|
^^^^
|
|
|
|
|
|
|
|
Most ArgumentParser actions add some value as an attribute of the object
|
|
|
|
returned by :meth:`parse_args`. The name of this attribute is determined by the
|
|
|
|
``dest`` keyword argument of :meth:`add_argument`. For positional argument
|
|
|
|
actions, ``dest`` is normally supplied as the first argument to
|
|
|
|
:meth:`add_argument`::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('bar')
|
|
|
|
>>> parser.parse_args('XXX'.split())
|
|
|
|
Namespace(bar='XXX')
|
|
|
|
|
|
|
|
For optional argument actions, the value of ``dest`` is normally inferred from
|
|
|
|
the option strings. ArgumentParser objects generate the value of ``dest`` by
|
|
|
|
taking the first long option string and stripping away the initial ``'--'``
|
|
|
|
string. If no long option strings were supplied, ``dest`` will be derived from
|
|
|
|
the first short option string by stripping the initial ``'-'`` character. Any
|
|
|
|
internal ``'-'`` characters will be converted to ``'_'`` characters to make sure
|
|
|
|
the string is a valid attribute name. The examples below illustrate this
|
|
|
|
behavior::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('-f', '--foo-bar', '--foo')
|
|
|
|
>>> parser.add_argument('-x', '-y')
|
|
|
|
>>> parser.parse_args('-f 1 -x 2'.split())
|
|
|
|
Namespace(foo_bar='1', x='2')
|
|
|
|
>>> parser.parse_args('--foo 1 -y 2'.split())
|
|
|
|
Namespace(foo_bar='1', x='2')
|
|
|
|
|
|
|
|
If you would like to use a different attribute name from the one automatically
|
|
|
|
inferred by the ArgumentParser, you can supply it with an explicit ``dest``
|
|
|
|
parameter::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', dest='bar')
|
|
|
|
>>> parser.parse_args('--foo XXX'.split())
|
|
|
|
Namespace(bar='XXX')
|
|
|
|
|
|
|
|
|
|
|
|
The parse_args() method
|
|
|
|
-----------------------
|
|
|
|
|
|
|
|
.. method:: parse_args([args], [namespace])
|
|
|
|
|
|
|
|
Convert the strings to objects and assign them as attributes of the
|
|
|
|
namespace. Return the populated namespace.
|
|
|
|
|
|
|
|
Previous calls to :meth:`add_argument` determine exactly what objects are
|
|
|
|
created and how they are assigned. See the documentation for
|
|
|
|
:meth:`add_argument` for details.
|
|
|
|
|
|
|
|
By default, the arg strings are taken from :data:`sys.argv`, and a new empty
|
|
|
|
``Namespace`` object is created for the attributes.
|
|
|
|
|
|
|
|
Option value syntax
|
|
|
|
^^^^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
The :meth:`parse_args` method supports several ways of specifying the value of
|
|
|
|
an option (if it takes one). In the simplest case, the option and its value are
|
|
|
|
passed as two separate arguments::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('-x')
|
|
|
|
>>> parser.add_argument('--foo')
|
|
|
|
>>> parser.parse_args('-x X'.split())
|
|
|
|
Namespace(foo=None, x='X')
|
|
|
|
>>> parser.parse_args('--foo FOO'.split())
|
|
|
|
Namespace(foo='FOO', x=None)
|
|
|
|
|
|
|
|
For long options (options with names longer than a single character), you may
|
|
|
|
also pass the option and value as a single command line argument, using ``=`` to
|
|
|
|
separate them::
|
|
|
|
|
|
|
|
>>> parser.parse_args('--foo=FOO'.split())
|
|
|
|
Namespace(foo='FOO', x=None)
|
|
|
|
|
|
|
|
For short options (options only one character long), you may simply concatenate
|
|
|
|
the option and its value::
|
|
|
|
|
|
|
|
>>> parser.parse_args('-xX'.split())
|
|
|
|
Namespace(foo=None, x='X')
|
|
|
|
|
|
|
|
You can also combine several short options together, using only a single ``-``
|
|
|
|
prefix, as long as only the last option (or none of them) requires a value::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('-x', action='store_true')
|
|
|
|
>>> parser.add_argument('-y', action='store_true')
|
|
|
|
>>> parser.add_argument('-z')
|
|
|
|
>>> parser.parse_args('-xyzZ'.split())
|
|
|
|
Namespace(x=True, y=True, z='Z')
|
|
|
|
|
|
|
|
|
|
|
|
Invalid arguments
|
|
|
|
^^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
While parsing the command-line, ``parse_args`` checks for a variety of errors,
|
|
|
|
including ambiguous options, invalid types, invalid options, wrong number of
|
|
|
|
positional arguments, etc. When it encounters such an error, it exits and
|
|
|
|
prints the error along with a usage message::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('--foo', type=int)
|
|
|
|
>>> parser.add_argument('bar', nargs='?')
|
|
|
|
|
|
|
|
>>> # invalid type
|
|
|
|
>>> parser.parse_args(['--foo', 'spam'])
|
|
|
|
usage: PROG [-h] [--foo FOO] [bar]
|
|
|
|
PROG: error: argument --foo: invalid int value: 'spam'
|
|
|
|
|
|
|
|
>>> # invalid option
|
|
|
|
>>> parser.parse_args(['--bar'])
|
|
|
|
usage: PROG [-h] [--foo FOO] [bar]
|
|
|
|
PROG: error: no such option: --bar
|
|
|
|
|
|
|
|
>>> # wrong number of arguments
|
|
|
|
>>> parser.parse_args(['spam', 'badger'])
|
|
|
|
usage: PROG [-h] [--foo FOO] [bar]
|
|
|
|
PROG: error: extra arguments found: badger
|
|
|
|
|
|
|
|
|
|
|
|
Arguments containing ``"-"``
|
|
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
The ``parse_args`` method attempts to give errors whenever the user has clearly
|
|
|
|
made a mistake, but some situations are inherently ambiguous. For example, the
|
|
|
|
command-line arg ``'-1'`` could either be an attempt to specify an option or an
|
|
|
|
attempt to provide a positional argument. The ``parse_args`` method is cautious
|
|
|
|
here: positional arguments may only begin with ``'-'`` if they look like
|
|
|
|
negative numbers and there are no options in the parser that look like negative
|
|
|
|
numbers::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('-x')
|
|
|
|
>>> parser.add_argument('foo', nargs='?')
|
|
|
|
|
|
|
|
>>> # no negative number options, so -1 is a positional argument
|
|
|
|
>>> parser.parse_args(['-x', '-1'])
|
|
|
|
Namespace(foo=None, x='-1')
|
|
|
|
|
|
|
|
>>> # no negative number options, so -1 and -5 are positional arguments
|
|
|
|
>>> parser.parse_args(['-x', '-1', '-5'])
|
|
|
|
Namespace(foo='-5', x='-1')
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('-1', dest='one')
|
|
|
|
>>> parser.add_argument('foo', nargs='?')
|
|
|
|
|
|
|
|
>>> # negative number options present, so -1 is an option
|
|
|
|
>>> parser.parse_args(['-1', 'X'])
|
|
|
|
Namespace(foo=None, one='X')
|
|
|
|
|
|
|
|
>>> # negative number options present, so -2 is an option
|
|
|
|
>>> parser.parse_args(['-2'])
|
|
|
|
usage: PROG [-h] [-1 ONE] [foo]
|
|
|
|
PROG: error: no such option: -2
|
|
|
|
|
|
|
|
>>> # negative number options present, so both -1s are options
|
|
|
|
>>> parser.parse_args(['-1', '-1'])
|
|
|
|
usage: PROG [-h] [-1 ONE] [foo]
|
|
|
|
PROG: error: argument -1: expected one argument
|
|
|
|
|
|
|
|
If you have positional arguments that must begin with ``'-'`` and don't look
|
|
|
|
like negative numbers, you can insert the pseudo-argument ``'--'`` which tells
|
|
|
|
``parse_args`` that everything after that is a positional argument::
|
|
|
|
|
|
|
|
>>> parser.parse_args(['--', '-f'])
|
|
|
|
Namespace(foo='-f', one=None)
|
|
|
|
|
|
|
|
|
|
|
|
Argument abbreviations
|
|
|
|
^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
The :meth:`parse_args` method allows you to abbreviate long options if the
|
|
|
|
abbreviation is unambiguous::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('-bacon')
|
|
|
|
>>> parser.add_argument('-badger')
|
|
|
|
>>> parser.parse_args('-bac MMM'.split())
|
|
|
|
Namespace(bacon='MMM', badger=None)
|
|
|
|
>>> parser.parse_args('-bad WOOD'.split())
|
|
|
|
Namespace(bacon=None, badger='WOOD')
|
|
|
|
>>> parser.parse_args('-ba BA'.split())
|
|
|
|
usage: PROG [-h] [-bacon BACON] [-badger BADGER]
|
|
|
|
PROG: error: ambiguous option: -ba could match -badger, -bacon
|
|
|
|
|
|
|
|
As you can see above, you will get an error if you pick a prefix that could
|
|
|
|
refer to more than one option.
|
|
|
|
|
|
|
|
|
|
|
|
Beyond ``sys.argv``
|
|
|
|
^^^^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
Sometimes it may be useful to have an ArgumentParser parse args other than those
|
|
|
|
of :data:`sys.argv`. This can be accomplished by passing a list of strings to
|
|
|
|
``parse_args``. You may have noticed that the examples in the argparse
|
|
|
|
documentation have made heavy use of this calling style - it is much easier to
|
|
|
|
use at the interactive prompt::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument(
|
|
|
|
... 'integers', metavar='int', type=int, choices=xrange(10),
|
|
|
|
... nargs='+', help='an integer in the range 0..9')
|
|
|
|
>>> parser.add_argument(
|
|
|
|
... '--sum', dest='accumulate', action='store_const', const=sum,
|
|
|
|
... default=max, help='sum the integers (default: find the max)')
|
|
|
|
>>> parser.parse_args(['1', '2', '3', '4'])
|
|
|
|
Namespace(accumulate=<built-in function max>, integers=[1, 2, 3, 4])
|
|
|
|
>>> parser.parse_args('1 2 3 4 --sum'.split())
|
|
|
|
Namespace(accumulate=<built-in function sum>, integers=[1, 2, 3, 4])
|
|
|
|
|
|
|
|
|
|
|
|
Custom namespaces
|
|
|
|
^^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
It may also be useful to have an ArgumentParser assign attributes to an already
|
|
|
|
existing object, rather than the newly-created Namespace object that is normally
|
|
|
|
used. This can be achieved by specifying the ``namespace=`` keyword argument::
|
|
|
|
|
|
|
|
>>> class C(object):
|
|
|
|
... pass
|
|
|
|
...
|
|
|
|
>>> c = C()
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo')
|
|
|
|
>>> parser.parse_args(args=['--foo', 'BAR'], namespace=c)
|
|
|
|
>>> c.foo
|
|
|
|
'BAR'
|
|
|
|
|
|
|
|
|
|
|
|
Other utilities
|
|
|
|
---------------
|
|
|
|
|
|
|
|
Sub-commands
|
|
|
|
^^^^^^^^^^^^
|
|
|
|
|
|
|
|
.. method:: add_subparsers()
|
|
|
|
|
|
|
|
A lot of programs split up their functionality into a number of sub-commands,
|
|
|
|
for example, the ``svn`` program can invoke sub-commands like ``svn
|
|
|
|
checkout``, ``svn update``, ``svn commit``, etc. Splitting up functionality
|
|
|
|
this way can be a particularly good idea when a program performs several
|
|
|
|
different functions which require different kinds of command-line arguments.
|
|
|
|
ArgumentParser objects support the creation of such sub-commands with the
|
|
|
|
:meth:`add_subparsers` method. The :meth:`add_subparsers` method is normally
|
|
|
|
called with no arguments and returns an special action object. This object
|
|
|
|
has a single method, ``add_parser``, which takes a command name and any
|
|
|
|
ArgumentParser constructor arguments, and returns an ArgumentParser object
|
|
|
|
that can be modified as usual.
|
|
|
|
|
|
|
|
Some example usage::
|
|
|
|
|
|
|
|
>>> # create the top-level parser
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> parser.add_argument('--foo', action='store_true', help='foo help')
|
|
|
|
>>> subparsers = parser.add_subparsers(help='sub-command help')
|
|
|
|
>>>
|
|
|
|
>>> # create the parser for the "a" command
|
|
|
|
>>> parser_a = subparsers.add_parser('a', help='a help')
|
|
|
|
>>> parser_a.add_argument('bar', type=int, help='bar help')
|
|
|
|
>>>
|
|
|
|
>>> # create the parser for the "b" command
|
|
|
|
>>> parser_b = subparsers.add_parser('b', help='b help')
|
|
|
|
>>> parser_b.add_argument('--baz', choices='XYZ', help='baz help')
|
|
|
|
>>>
|
|
|
|
>>> # parse some arg lists
|
|
|
|
>>> parser.parse_args(['a', '12'])
|
|
|
|
Namespace(bar=12, foo=False)
|
|
|
|
>>> parser.parse_args(['--foo', 'b', '--baz', 'Z'])
|
|
|
|
Namespace(baz='Z', foo=True)
|
|
|
|
|
|
|
|
Note that the object returned by :meth:`parse_args` will only contain
|
|
|
|
attributes for the main parser and the subparser that was selected by the
|
|
|
|
command line (and not any other subparsers). So in the example above, when
|
|
|
|
the ``"a"`` command is specified, only the ``foo`` and ``bar`` attributes are
|
|
|
|
present, and when the ``"b"`` command is specified, only the ``foo`` and
|
|
|
|
``baz`` attributes are present.
|
|
|
|
|
|
|
|
Similarly, when a help message is requested from a subparser, only the help
|
|
|
|
for that particular parser will be printed. The help message will not
|
|
|
|
include parent parser or sibling parser messages. (You can however supply a
|
|
|
|
help message for each subparser command by suppling the ``help=`` argument to
|
|
|
|
``add_parser`` as above.)
|
|
|
|
|
|
|
|
::
|
|
|
|
|
|
|
|
>>> parser.parse_args(['--help'])
|
|
|
|
usage: PROG [-h] [--foo] {a,b} ...
|
|
|
|
|
|
|
|
positional arguments:
|
|
|
|
{a,b} sub-command help
|
|
|
|
a a help
|
|
|
|
b b help
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--foo foo help
|
|
|
|
|
|
|
|
>>> parser.parse_args(['a', '--help'])
|
|
|
|
usage: PROG a [-h] bar
|
|
|
|
|
|
|
|
positional arguments:
|
|
|
|
bar bar help
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
|
|
|
|
>>> parser.parse_args(['b', '--help'])
|
|
|
|
usage: PROG b [-h] [--baz {X,Y,Z}]
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
--baz {X,Y,Z} baz help
|
|
|
|
|
|
|
|
The :meth:`add_subparsers` method also supports ``title`` and ``description``
|
|
|
|
keyword arguments. When either is present, the subparser's commands will
|
|
|
|
appear in their own group in the help output. For example::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> subparsers = parser.add_subparsers(title='subcommands',
|
|
|
|
... description='valid subcommands',
|
|
|
|
... help='additional help')
|
|
|
|
>>> subparsers.add_parser('foo')
|
|
|
|
>>> subparsers.add_parser('bar')
|
|
|
|
>>> parser.parse_args(['-h'])
|
|
|
|
usage: [-h] {foo,bar} ...
|
|
|
|
|
|
|
|
optional arguments:
|
|
|
|
-h, --help show this help message and exit
|
|
|
|
|
|
|
|
subcommands:
|
|
|
|
valid subcommands
|
|
|
|
|
|
|
|
{foo,bar} additional help
|
|
|
|
|
|
|
|
|
|
|
|
One particularly effective way of handling sub-commands is to combine the use
|
|
|
|
of the :meth:`add_subparsers` method with calls to :meth:`set_defaults` so
|
|
|
|
that each subparser knows which Python function it should execute. For
|
|
|
|
example::
|
|
|
|
|
|
|
|
>>> # sub-command functions
|
|
|
|
>>> def foo(args):
|
|
|
|
... print args.x * args.y
|
|
|
|
...
|
|
|
|
>>> def bar(args):
|
|
|
|
... print '((%s))' % args.z
|
|
|
|
...
|
|
|
|
>>> # create the top-level parser
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> subparsers = parser.add_subparsers()
|
|
|
|
>>>
|
|
|
|
>>> # create the parser for the "foo" command
|
|
|
|
>>> parser_foo = subparsers.add_parser('foo')
|
|
|
|
>>> parser_foo.add_argument('-x', type=int, default=1)
|
|
|
|
>>> parser_foo.add_argument('y', type=float)
|
|
|
|
>>> parser_foo.set_defaults(func=foo)
|
|
|
|
>>>
|
|
|
|
>>> # create the parser for the "bar" command
|
|
|
|
>>> parser_bar = subparsers.add_parser('bar')
|
|
|
|
>>> parser_bar.add_argument('z')
|
|
|
|
>>> parser_bar.set_defaults(func=bar)
|
|
|
|
>>>
|
|
|
|
>>> # parse the args and call whatever function was selected
|
|
|
|
>>> args = parser.parse_args('foo 1 -x 2'.split())
|
|
|
|
>>> args.func(args)
|
|
|
|
2.0
|
|
|
|
>>>
|
|
|
|
>>> # parse the args and call whatever function was selected
|
|
|
|
>>> args = parser.parse_args('bar XYZYX'.split())
|
|
|
|
>>> args.func(args)
|
|
|
|
((XYZYX))
|
|
|
|
|
|
|
|
This way, you can let :meth:`parse_args` do all the work for you, and then
|
|
|
|
just call the appropriate function after the argument parsing is complete.
|
|
|
|
Associating functions with actions like this is typically the easiest way to
|
|
|
|
handle the different actions for each of your subparsers. However, if you
|
|
|
|
find it necessary to check the name of the subparser that was invoked, you
|
|
|
|
can always provide a ``dest`` keyword argument to the :meth:`add_subparsers`
|
|
|
|
call::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> subparsers = parser.add_subparsers(dest='subparser_name')
|
|
|
|
>>> subparser1 = subparsers.add_parser('1')
|
|
|
|
>>> subparser1.add_argument('-x')
|
|
|
|
>>> subparser2 = subparsers.add_parser('2')
|
|
|
|
>>> subparser2.add_argument('y')
|
|
|
|
>>> parser.parse_args(['2', 'frobble'])
|
|
|
|
Namespace(subparser_name='2', y='frobble')
|
|
|
|
|
|
|
|
|
|
|
|
FileType objects
|
|
|
|
^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
.. class:: FileType(mode='r', bufsize=None)
|
|
|
|
|
|
|
|
The :class:`FileType` factory creates objects that can be passed to the type
|
|
|
|
argument of :meth:`add_argument`. Arguments that have :class:`FileType`
|
|
|
|
objects as their type will open command-line args as files with the requested
|
|
|
|
modes and buffer sizes:
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--output', type=argparse.FileType('wb', 0))
|
|
|
|
>>> parser.parse_args(['--output', 'out'])
|
|
|
|
Namespace(output=<open file 'out', mode 'wb' at 0x...>)
|
|
|
|
|
|
|
|
FileType objects understand the pseudo-argument ``'-'`` and automatically
|
|
|
|
convert this into ``sys.stdin`` for readable :class:`FileType` objects and
|
|
|
|
``sys.stdout`` for writable :class:`FileType` objects:
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('infile', type=argparse.FileType('r'))
|
|
|
|
>>> parser.parse_args(['-'])
|
|
|
|
Namespace(infile=<open file '<stdin>', mode 'r' at 0x...>)
|
|
|
|
|
|
|
|
|
|
|
|
Argument groups
|
|
|
|
^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
.. method:: add_argument_group([title], [description])
|
|
|
|
|
|
|
|
By default, ArgumentParser objects group command-line arguments into
|
|
|
|
"positional arguments" and "optional arguments" when displaying help
|
|
|
|
messages. When there is a better conceptual grouping of arguments than this
|
|
|
|
default one, appropriate groups can be created using the
|
|
|
|
:meth:`add_argument_group` method::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG', add_help=False)
|
|
|
|
>>> group = parser.add_argument_group('group')
|
|
|
|
>>> group.add_argument('--foo', help='foo help')
|
|
|
|
>>> group.add_argument('bar', help='bar help')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: PROG [--foo FOO] bar
|
|
|
|
|
|
|
|
group:
|
|
|
|
bar bar help
|
|
|
|
--foo FOO foo help
|
|
|
|
|
|
|
|
The :meth:`add_argument_group` method returns an argument group object which
|
|
|
|
has an :meth:`add_argument` method just like a regular ArgumentParser
|
|
|
|
objects. When an argument is added to the group, the parser treats it just
|
|
|
|
like a normal argument, but displays the argument in a separate group for
|
|
|
|
help messages. The :meth:`add_argument_group` method accepts ``title`` and
|
|
|
|
``description`` arguments which can be used to customize this display::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG', add_help=False)
|
|
|
|
>>> group1 = parser.add_argument_group('group1', 'group1 description')
|
|
|
|
>>> group1.add_argument('foo', help='foo help')
|
|
|
|
>>> group2 = parser.add_argument_group('group2', 'group2 description')
|
|
|
|
>>> group2.add_argument('--bar', help='bar help')
|
|
|
|
>>> parser.print_help()
|
|
|
|
usage: PROG [--bar BAR] foo
|
|
|
|
|
|
|
|
group1:
|
|
|
|
group1 description
|
|
|
|
|
|
|
|
foo foo help
|
|
|
|
|
|
|
|
group2:
|
|
|
|
group2 description
|
|
|
|
|
|
|
|
--bar BAR bar help
|
|
|
|
|
|
|
|
Note that any arguments not in your user defined groups will end up back in
|
|
|
|
the usual "positional arguments" and "optional arguments" sections.
|
|
|
|
|
|
|
|
|
|
|
|
Mutual exclusion
|
|
|
|
^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
.. method:: add_mutually_exclusive_group([required=False])
|
|
|
|
|
|
|
|
Sometimes, you need to make sure that only one of a couple different options
|
|
|
|
is specified on the command line. You can create groups of such mutually
|
|
|
|
exclusive arguments using the :meth:`add_mutually_exclusive_group` method.
|
|
|
|
When :func:`parse_args` is called, argparse will make sure that only one of
|
|
|
|
the arguments in the mutually exclusive group was present on the command
|
|
|
|
line::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> group = parser.add_mutually_exclusive_group()
|
|
|
|
>>> group.add_argument('--foo', action='store_true')
|
|
|
|
>>> group.add_argument('--bar', action='store_false')
|
|
|
|
>>> parser.parse_args(['--foo'])
|
|
|
|
Namespace(bar=True, foo=True)
|
|
|
|
>>> parser.parse_args(['--bar'])
|
|
|
|
Namespace(bar=False, foo=False)
|
|
|
|
>>> parser.parse_args(['--foo', '--bar'])
|
|
|
|
usage: PROG [-h] [--foo | --bar]
|
|
|
|
PROG: error: argument --bar: not allowed with argument --foo
|
|
|
|
|
|
|
|
The :meth:`add_mutually_exclusive_group` method also accepts a ``required``
|
|
|
|
argument, to indicate that at least one of the mutually exclusive arguments
|
|
|
|
is required::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser(prog='PROG')
|
|
|
|
>>> group = parser.add_mutually_exclusive_group(required=True)
|
|
|
|
>>> group.add_argument('--foo', action='store_true')
|
|
|
|
>>> group.add_argument('--bar', action='store_false')
|
|
|
|
>>> parser.parse_args([])
|
|
|
|
usage: PROG [-h] (--foo | --bar)
|
|
|
|
PROG: error: one of the arguments --foo --bar is required
|
|
|
|
|
|
|
|
Note that currently mutually exclusive argument groups do not support the
|
|
|
|
``title`` and ``description`` arguments of :meth:`add_argument_group`. This
|
|
|
|
may change in the future however, so you are *strongly* recommended to
|
|
|
|
specify ``required`` as a keyword argument if you use it.
|
|
|
|
|
|
|
|
|
|
|
|
Parser defaults
|
|
|
|
^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
.. method:: set_defaults(**kwargs)
|
|
|
|
|
|
|
|
Most of the time, the attributes of the object returned by :meth:`parse_args`
|
|
|
|
will be fully determined by inspecting the command-line args and the argument
|
|
|
|
actions described in your :meth:`add_argument` calls. However, sometimes it
|
|
|
|
may be useful to add some additional attributes that are determined without
|
|
|
|
any inspection of the command-line. The :meth:`set_defaults` method allows
|
|
|
|
you to do this::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('foo', type=int)
|
|
|
|
>>> parser.set_defaults(bar=42, baz='badger')
|
|
|
|
>>> parser.parse_args(['736'])
|
|
|
|
Namespace(bar=42, baz='badger', foo=736)
|
|
|
|
|
|
|
|
Note that parser-level defaults always override argument-level defaults. So
|
|
|
|
if you set a parser-level default for a name that matches an argument, the
|
|
|
|
old argument default will no longer be used::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', default='bar')
|
|
|
|
>>> parser.set_defaults(foo='spam')
|
|
|
|
>>> parser.parse_args([])
|
|
|
|
Namespace(foo='spam')
|
|
|
|
|
|
|
|
Parser-level defaults can be particularly useful when you're working with
|
|
|
|
multiple parsers. See the :meth:`add_subparsers` method for an example of
|
|
|
|
this type.
|
|
|
|
|
|
|
|
.. method:: get_default(dest)
|
|
|
|
|
|
|
|
Get the default value for a namespace attribute, as set by either
|
|
|
|
:meth:`add_argument` or by :meth:`set_defaults`::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', default='badger')
|
|
|
|
>>> parser.get_default('foo')
|
|
|
|
'badger'
|
|
|
|
|
|
|
|
|
|
|
|
Printing help
|
|
|
|
^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
In most typical applications, :meth:`parse_args` will take care of formatting
|
|
|
|
and printing any usage or error messages. However, should you want to format or
|
|
|
|
print these on your own, several methods are available:
|
|
|
|
|
|
|
|
.. method:: print_usage([file]):
|
|
|
|
|
|
|
|
Print a brief description of how the :class:`ArgumentParser` should be
|
|
|
|
invoked on the command line. If ``file`` is not present, ``sys.stderr`` is
|
|
|
|
assumed.
|
|
|
|
|
|
|
|
.. method:: print_help([file]):
|
|
|
|
|
|
|
|
Print a help message, including the program usage and information about the
|
|
|
|
arguments registered with the :class:`ArgumentParser`. If ``file`` is not
|
|
|
|
present, ``sys.stderr`` is assumed.
|
|
|
|
|
|
|
|
There are also variants of these methods that simply return a string instead of
|
|
|
|
printing it:
|
|
|
|
|
|
|
|
.. method:: format_usage():
|
|
|
|
|
|
|
|
Return a string containing a brief description of how the
|
|
|
|
:class:`ArgumentParser` should be invoked on the command line.
|
|
|
|
|
|
|
|
.. method:: format_help():
|
|
|
|
|
|
|
|
Return a string containing a help message, including the program usage and
|
|
|
|
information about the arguments registered with the :class:`ArgumentParser`.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Partial parsing
|
|
|
|
^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
.. method:: parse_known_args([args], [namespace])
|
|
|
|
|
|
|
|
Sometimes a script may only parse a few of the command line arguments, passing
|
|
|
|
the remaining arguments on to another script or program. In these cases, the
|
|
|
|
:meth:`parse_known_args` method can be useful. It works much like
|
|
|
|
:meth:`parse_args` except that it does not produce an error when extra arguments
|
|
|
|
are present. Instead, it returns a two item tuple containing the populated
|
|
|
|
namespace and the list of remaining argument strings.
|
|
|
|
|
|
|
|
::
|
|
|
|
|
|
|
|
>>> parser = argparse.ArgumentParser()
|
|
|
|
>>> parser.add_argument('--foo', action='store_true')
|
|
|
|
>>> parser.add_argument('bar')
|
|
|
|
>>> parser.parse_known_args(['--foo', '--badger', 'BAR', 'spam'])
|
|
|
|
(Namespace(bar='BAR', foo=True), ['--badger', 'spam'])
|
|
|
|
|
|
|
|
|
|
|
|
Customizing file parsing
|
|
|
|
^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
|
|
|
|
.. method:: convert_arg_line_to_args(arg_line)
|
|
|
|
|
|
|
|
Arguments that are read from a file (see the ``fromfile_prefix_chars``
|
|
|
|
keyword argument to the :class:`ArgumentParser` constructor) are read one
|
|
|
|
argument per line. If you need fancier parsing, then you can subclass the
|
|
|
|
:class:`ArgumentParser` and override the :meth:`convert_arg_line_to_args`
|
|
|
|
method.
|
|
|
|
|
|
|
|
This method takes a single argument ``arg_line`` which is a string read from
|
|
|
|
the argument file. It returns a list of arguments parsed from this string.
|
|
|
|
The method is called once per line read from the argument file, in order.
|
|
|
|
|
|
|
|
A useful override of this method is one that treats each space-separated word
|
|
|
|
as an argument::
|
|
|
|
|
|
|
|
def convert_arg_line_to_args(self, arg_line):
|
|
|
|
for arg in arg_line.split():
|
|
|
|
if not arg.strip():
|
|
|
|
continue
|
|
|
|
yield arg
|
|
|
|
|
|
|
|
|
|
|
|
Upgrading optparse code
|
|
|
|
-----------------------
|
|
|
|
|
|
|
|
Originally, the argparse module had attempted to maintain compatibility with
|
|
|
|
optparse. However, optparse was difficult to extend transparently, particularly
|
|
|
|
with the changes required to support the new ``nargs=`` specifiers and better
|
|
|
|
usage messges. When most everything in optparse had either been copy-pasted
|
|
|
|
over or monkey-patched, it no longer seemed practical to try to maintain the
|
|
|
|
backwards compatibility.
|
|
|
|
|
|
|
|
A partial upgrade path from optparse to argparse:
|
|
|
|
|
|
|
|
* Replace all ``add_option()`` calls with :meth:`add_argument` calls.
|
|
|
|
|
|
|
|
* Replace ``options, args = parser.parse_args()`` with ``args =
|
|
|
|
parser.parse_args()`` and add additional :meth:`add_argument` calls for the
|
|
|
|
positional arguments.
|
|
|
|
|
|
|
|
* Replace callback actions and the ``callback_*`` keyword arguments with
|
|
|
|
``type`` or ``action`` arguments.
|
|
|
|
|
|
|
|
* Replace string names for ``type`` keyword arguments with the corresponding
|
|
|
|
type objects (e.g. int, float, complex, etc).
|
|
|
|
|
|
|
|
* Replace ``Values`` with ``Namespace`` and ``OptionError/OptionValueError``
|
|
|
|
with ``ArgumentError``.
|
|
|
|
|
|
|
|
* Replace strings with implicit arguments such as ``%default`` or ``%prog`` with
|
|
|
|
the standard python syntax to use dictionaries to format strings, that is,
|
|
|
|
``%(default)s`` and ``%(prog)s``.
|