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Pythonic command line arguments parser, that will make you smile
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README.md

docopt creates beautiful command-line interfaces

New in version 0.4.0:

  • option descriptions become optional,
  • support for "--" and "-" commands.

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:

"""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 ussage 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 recommends putting help message in the module docstrings.

Installation

Use pip or easy_install:

pip install docopt

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

docopt is tested with Python 2.5, 2.6, 2.7, 3.1, 3.2.

API

from docopt import docopt

arguments = docopt(doc, argv=sys.argv[1:], help=True, version=None)

docopt takes 1 required and 3 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::
"""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 it is the argument vector passed to your program (sys.argv[1:]). You can supply it with the list of strings (similar to sys.argv) e.g. ['--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.

The return value is just a dictionary with options, arguments and commands, with keys spelled exactly like in a 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::

{'--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'}

This turns out to be the most straight-forward, unambiguous and readable format possible. You can instantly see that args['<name>'] is an argument, args['--speed'] is an option, and args['move'] is a command.

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. Also, take a look at the beautiful examples.

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::

"""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::

"""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 for option to have an argument, a default value, or specify synonymous short/long versions of 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) mutualy exclussive elements. Group them using ( ) if one of the mutually exclussive 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 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 you usage patterns.
  • "[-]". Single dash "-" is used by convention to signify that stdin is used instead of a file. To support this add "[-]" to you usage patterns. "-" act as a normal command.

If your usage patterns allow to match the same-named argument several times, parser will put the matched values into a list, e.g. in case the pattern is my-program.py FILE FILE then args['FILE'] will be a list; in case the pattern is my-program.py FILE... it will also be a list.

Option descriptions format

Option descriptions consist of a list of options that you put below your ussage 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 <file>, --input <file>   # with comma, wihtout "=" sing
    
  • 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: ./]
    

Development

We would love to hear what you think about docopt on our issues page.

Contribute, make pull requrests, 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 beyound the Python community!

Help develop Ruby port, CoffeeScript port, Lua port or create a port for your favorite language! You are encouraged to use the Python version as a reference implementation. A Language-agnostic test suite is bundled with Python implementation.

Porting discussion is on issues page.

Changelog

docopt follows semantic versioning. The first release with stable API will be 1.0 (soon). Until then, you are encouraged to specify explicitly the version in your dependency tools, e.g.:

pip install docopt==0.4.0
  • 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. Incompatible changes: docopt returns dictionary.
  • 0.2.0 Usage pattern matching. Positional arguments parsing based on usage patterns. Incompatible changes: docopt returns namespace (for arguments), not list. Usage pattern is formalized.
  • 0.1.0 Initial release. Options-parsing only (based on options description).
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