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 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 ...]. Ellipsis
  works as a unary operator on the expression to the left.
• [options] (case sensitive) shortcut for any options. You can
  use it if you want to specify that the usage pattern could be
  provided with any options defined below in the option-descriptions
  and do not want to enumerate them all in usage-pattern.
• "[--]". Double dash "--" is used by convention to separate
  positional arguments that can be mistaken for options. In order to
  support this convention add "[--]" to your usage patterns.
• "[-]". Single dash "-" is used by convention to signify that
  stdin is used instead of a file. To support this add "[-]"
  to your usage patterns. "-" acts as a normal command.

If your pattern allows to match argument-less option (a flag) several
times::

Usage: my_program.py [-v, -vv, -vvv]

then number of occurrences of the option will be counted. I.e.
args['-v'] will be 2 if program was invoked as my_program -vv. Same works for commands.

If your usage patterns allows to match same-named option with argument
or positional argument several times, the matched arguments will be
collected into a list::

Usage: my_program.py <file> <file> --path=<path>...

I.e. invoked with my_program.py file1 file2 --path=./here --path=./there the returned dict will contain args['<file>'] == ['file1', 'file2'] and args['--path'] == ['./here', './there'].

Option descriptions format

Option descriptions consist of a list of options that you put
below your usage patterns.

It is necessary to list option descriptions in order to specify:

• synonymous short and long options,
• if an option has an argument,
• if option's argument has a default value.

The rules are as follows:

• Every line in doc that starts with - or -- (not counting
  spaces) is treated as an option description, e.g.::

  Options:
  --verbose # GOOD
  -o FILE # GOOD
  Other: --bad # BAD, line does not start with dash "-"

• To specify that option has an argument, put a word describing that
  argument after space (or equals "=" sign) as shown below. Follow
  either or UPPER-CASE convention for options'
  arguments. You can use comma if you want to separate options. In
  the example below, both lines are valid, however you are recommended
  to stick to a single style.::

  -o FILE --output=FILE # without comma, with "=" sign
  -i , --input # with comma, without "=" sign

• Use two spaces to separate options with their informal description::

  --verbose More text. # BAD, will be treated as if verbose option had
  # an argument "More", so use 2 spaces instead
  -q Quit. # GOOD
  -o FILE Output file. # GOOD
  --stdout Use stdout. # GOOD, 2 spaces

• If you want to set a default value for an option with an argument,
  put it into the option-description, in form [default: <my-default-value>]::

  --coefficient=K The K coefficient [default: 2.95]
  --output=FILE Output file [default: test.txt]
  --directory=DIR Some directory [default: ./]

• If the option is not repeatable, the value inside [default: ...]
  will be interpreted as string. If it is repeatable, it will be
  splited into a list on whitespace::

  Usage: my_program.py [--repeatable= --repeatable=]
  [--another-repeatable=]...
  [--not-repeatable=]

  will be ['./here', './there']

  --repeatable= [default: ./here ./there]

  will be ['./here']

  --another-repeatable= [default: ./here]

  will be './here ./there', because it is not repeatable

  --not-repeatable= [default: ./here ./there]

Examples

We have an extensive list of examples <https://github.com/docopt/docopt/tree/master/examples>_ which cover
every aspect of functionality of docopt. Try them out, read the
source if in doubt.

Subparsers, multi-level help and huge applications (like git)

If you want to split your usage-pattern into several, implement
multi-level help (with separate help-screen for each subcommand),
want to interface with existing scripts that don't use docopt, or
you're building the next "git", you will need the new options_first
parameter (described in API section above). To get you started quickly
we implemented a subset of git command-line interface as an example:
examples/git <https://github.com/docopt/docopt/tree/master/examples/git>_

Data validation

docopt does one thing and does it well: it implements your
command-line interface. However it does not validate the input data.
On the other hand there are libraries like python schema <https://github.com/halst/schema>_ which make validating data a
breeze. Take a look at validation_example.py <https://github.com/docopt/docopt/tree/master/examples/validation_example.py>_
which uses schema to validate data and report an error to the
user.

Using docopt with config-files

Often configuration files are used to provide default values which
could be overriden by command-line arguments. Since docopt
returns a simple dictionary it is very easy to integrate with
config-files written in JSON, YAML or INI formats.
config_file_example.py <examples/config_file_example.py>_ provides
and example of how to use docopt with JSON or INI config-file.

Development

We would love to hear what you think about docopt on our issues page <http://github.com/docopt/docopt/issues>_

Make pull requests, report bugs, suggest ideas and discuss
docopt. You can also drop a line directly to
vladimir@keleshev.com.

Porting docopt to other languages

We think docopt is so good, we want to share it beyond the Python
community! All official docopt ports to other languages can be found
under the docopt organization page <http://github.com/docopt>_
on GitHub.

If your favourite language isn't among then, you can always create a
port for it! You are encouraged to use the Python version as a
reference implementation. A Language-agnostic test suite is bundled
with Python implementation <http://github.com/docopt/docopt>_.

Porting discussion is on issues page <http://github.com/docopt/docopt/issues>_.

Changelog

docopt follows semantic versioning <http://semver.org>_. The
first release with stable API will be 1.0.0 (soon). Until then, you
are encouraged to specify explicitly the version in your dependency
tools, e.g.::

pip install docopt==0.6.2

• 0.6.2 Bugfix release.
• 0.6.1 Bugfix release.
• 0.6.0 options_first parameter.
  Breaking changes: Corrected [options] meaning.
  argv defaults to None.
• 0.5.0 Repeated options/commands are counted or accumulated into a
  list.
• 0.4.2 Bugfix release.
• 0.4.0 Option descriptions become optional,
  support for "--" and "-" commands.
• 0.3.0 Support for (sub)commands like git remote add.
  Introduce [options] shortcut for any options.
  Breaking changes: docopt returns dictionary.
• 0.2.0 Usage pattern matching. Positional arguments parsing based on
  usage patterns.
  Breaking changes: docopt returns namespace (for arguments),
  not list. Usage pattern is formalized.
• 0.1.0 Initial release. Options-parsing only (based on options
  description).