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docopt-ng creates beautiful command-line interfaces

Test codecov image Jazzband Ruff

docopt-ng is a fork of the original docopt, now maintained by the jazzband project. Now with maintenance, typehints, and complete test coverage!

docopt-ng helps you create beautiful command-line interfaces:

"""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__":
    argv = ["ship", "Guardian", "move", "100", "150", "--speed=15"]
    arguments = docopt(__doc__, argv)
    print(arguments)

results in:

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

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 recommends putting help message in the module docstrings.

Installation

Use pip:

python -m pip install docopt-ng

docopt-ng is tested with Python 3.7+.

API

def docopt(
    docstring: str,
    argv: list[str] | str | None = None,
    default_help: bool = True,
    version: Any = None,
    options_first: bool = False,
) -> ParsedOptions:

docopt takes a docstring, and 4 optional arguments:

  • docstring is a string that contains a help message that will be used to create the option parser. The simple rules of how to write such a help message are given in next sections. Typically you would just use __doc__.

  • 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"], or a single string that will be split on spaces like "--verbose -o hai.txt".

  • default_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. Furthermore, dot notation is supported, with preceeding dashes (-) and surrounding brackets (<>) ignored, for example arguments.drifting or arguments.x.

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:

"""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. 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 <angular-brackets> 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, 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=<arg> --repeatable=<arg>]
                     [--another-repeatable=<arg>]...
                     [--not-repeatable=<arg>]

# will be ["./here", "./there"]
--repeatable=<arg>          [default: ./here ./there]

# will be ["./here"]
--another-repeatable=<arg>  [default: ./here]

# will be "./here ./there", because it is not repeatable
--not-repeatable=<arg>      [default: ./here ./there]

Examples

We have an extensive list of examples which cover every aspect of functionality of docopt-ng. Try them out, read the source if in doubt.

Development

We would love to hear what you think about docopt-ng on our issues page. Make pull requests, report bugs, and suggest ideas.

To setup your dev environment, fork this repo and clone it locally. We use pdm to manage the project, so install that first.

Then create a virtual env, install dev requirements and the package itself as editable, then install the pre-commit hooks:

pdm sync --dev --group dev
pdm run pre-commit install

Useful testing, linting, and formatting commands:

pdm run pytest
pdm run ruff check .
pdm run ruff format .