docopt creates beautiful command-line interfaces

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Video introduction to docopt: PyCon UK 2012: Create *beautiful* command-line interfaces with Python <http://youtu.be/pXhcPJK5cMc>_

New in version 0.6.1:

- Fix issue `#85 <https://github.com/docopt/docopt/issues/85>`_
  which caused improper handling of ``[options]`` shortcut
  if it was present several times.

New in version 0.6.0:

- New argument ``options_first``, disallows interspersing options
  and arguments.  If you supply ``options_first=True`` to
  ``docopt``, it will interpret all arguments as positional
  arguments after first positional argument.

- If option with argument could be repeated, its default value
  will be interpreted as space-separated list. E.g. with
  ``[default: ./here ./there]`` will be interpreted as
  ``['./here', './there']``.

Breaking changes:

- Meaning of ``[options]`` shortcut slightly changed. Previously
  it meant *"any known option"*. Now it means *"any option not in
  usage-pattern"*.  This avoids the situation when an option is
  allowed to be repeated unintentionally.

- ``argv`` is ``None`` by default, not ``sys.argv[1:]``.
  This allows ``docopt`` to always use the *latest* ``sys.argv``,
  not ``sys.argv`` during import time.

Isn't it awesome how optparse and argparse generate help messages based on your code?!

Hell no! You know what's awesome? It's when the option parser is generated based on the beautiful help message that you write yourself! This way you don't need to write this stupid repeatable parser-code, and instead can write only the help message--the way you want it.

docopt helps you create most beautiful command-line interfaces easily:

.. code:: python

"""Naval Fate.

Usage:
  naval_fate.py ship new <name>...
  naval_fate.py ship <name> move <x> <y> [--speed=<kn>]
  naval_fate.py ship shoot <x> <y>
  naval_fate.py mine (set|remove) <x> <y> [--moored | --drifting]
  naval_fate.py (-h | --help)
  naval_fate.py --version

Options:
  -h --help     Show this screen.
  --version     Show version.
  --speed=<kn>  Speed in knots [default: 10].
  --moored      Moored (anchored) mine.
  --drifting    Drifting mine.

"""
from docopt import docopt


if __name__ == '__main__':
    arguments = docopt(__doc__, version='Naval Fate 2.0')
    print(arguments)

Beat that! The option parser is generated based on the docstring above that is passed to docopt function. docopt parses the usage pattern ("Usage: ...") and option descriptions (lines starting with dash "-") and ensures that the program invocation matches the usage pattern; it parses options, arguments and commands based on that. The basic idea is that a good help message has all necessary information in it to make a parser.

Also, PEP 257 <http://www.python.org/dev/peps/pep-0257/>_ recommends putting help message in the module docstrings.

Installation

Use pip <http://pip-installer.org>_ or easy_install::

pip install docopt==0.6.2

Alternatively, you can just drop docopt.py file into your project--it is self-contained.

docopt is tested with Python 2.7, 3.4, 3.5, and 3.6.

Testing

You can run unit tests using the command:

python setup.py test

API

.. code:: python

from docopt import docopt

.. code:: python

docopt(doc, argv=None, help=True, version=None, options_first=False)

docopt takes 1 required and 4 optional arguments:

• doc could be a module docstring (__doc__) or some other string that contains a help message that will be parsed to create the option parser. The simple rules of how to write such a help message are given in next sections. Here is a quick example of such a string:

.. code:: python

"""Usage: my_program.py [-hso FILE] [--quiet | --verbose] [INPUT ...]

-h --help    show this
-s --sorted  sorted output
-o FILE      specify output file [default: ./test.txt]
--quiet      print less text
--verbose    print more text

"""

• argv is an optional argument vector; by default docopt uses the argument vector passed to your program (sys.argv[1:]). Alternatively you can supply a list of strings like ['--verbose', '-o', 'hai.txt'].

• help, by default True, specifies whether the parser should automatically print the help message (supplied as doc) and terminate, in case -h or --help option is encountered (options should exist in usage pattern, more on that below). If you want to handle -h or --help options manually (as other options), set help=False.

• version, by default None, is an optional argument that specifies the version of your program. If supplied, then, (assuming --version option is mentioned in usage pattern) when parser encounters the --version option, it will print the supplied version and terminate. version could be any printable object, but most likely a string, e.g. "2.1.0rc1".

  Note, when docopt is set to automatically handle -h, --help and --version options, you still need to mention them in usage pattern for this to work. Also, for your users to know about them.

• options_first, by default False. If set to True will disallow mixing options and positional argument. I.e. after first positional argument, all arguments will be interpreted as positional even if the look like options. This can be used for strict compatibility with POSIX, or if you want to dispatch your arguments to other programs.

The return value is a simple dictionary with options, arguments and commands as keys, spelled exactly like in your help message. Long versions of options are given priority. For example, if you invoke the top example as::

naval_fate.py ship Guardian move 100 150 --speed=15

the return dictionary will be:

.. code:: python

{'--drifting': False,    'mine': False,
 '--help': False,        'move': True,
 '--moored': False,      'new': False,
 '--speed': '15',        'remove': False,
 '--version': False,     'set': False,
 '<name>': ['Guardian'], 'ship': True,
 '<x>': '100',           'shoot': False,
 '<y>': '150'}

Help message format

Help message consists of 2 parts:

• Usage pattern, e.g.::

  Usage: my_program.py [-hso FILE] [--quiet | --verbose] [INPUT ...]

• Option descriptions, e.g.::

  -h --help show this -s --sorted sorted output -o FILE specify output file [default: ./test.txt] --quiet print less text --verbose print more text

Their format is described below; other text is ignored.

Usage pattern format

Usage pattern is a substring of doc that starts with usage: (case insensitive) and ends with a visibly empty line. Minimum example:

.. code:: python

"""Usage: my_program.py

"""

The first word after usage: is interpreted as your program's name. You can specify your program's name several times to signify several exclusive patterns:

.. code:: python

"""Usage: my_program.py FILE
          my_program.py COUNT FILE

"""

Each pattern can consist of the following elements:

• <arguments>, ARGUMENTS. Arguments are specified as either upper-case words, e.g. my_program.py CONTENT-PATH or words surrounded by angular brackets: my_program.py <content-path>.
• --options. Options are words started with dash (-), e.g. --output, -o. You can "stack" several of one-letter options, e.g. -oiv which will be the same as -o -i -v. The options can have arguments, e.g. --input=FILE or -i FILE or even -iFILE. However it is important that you specify option descriptions if you want your option to have an argument, a default value, or specify synonymous short/long versions of the option (see next section on option descriptions).
• commands are words that do not follow the described above conventions of --options or <arguments> or ARGUMENTS, plus two special commands: dash "-" and double dash "--" (see below).

Use the following constructs to specify patterns:

• [ ] (brackets) optional elements. e.g.: my_program.py [-hvqo FILE]
• ( ) (parens) required elements. All elements that are not put in [ ] are also required, e.g.: my_program.py --path=<path> <file>... is the same as my_program.py (--path=<path> <file>...). (Note, "required options" might be not a good idea for your users).
• | (pipe) mutually exclusive elements. Group them using ( ) if one of the mutually exclusive elements is required: my_program.py (--clockwise | --counter-clockwise) TIME. Group them using [ ] if none of the mutually-exclusive elements are required: my_program.py [--left | --right].
• ... (ellipsis) one or more elements. To specify that arbitrary number of repeating elements could be accepted, use ellipsis (...), e.g. my_program.py FILE ... means one or more FILE-s are accepted. If you want to accept zero or more elements, use brackets, e.g.: my_program.py [FILE ...]