Note
New in version 0.3.0: (sub)commands support, [options] shortcut.
Warning
Incompatible change in 0.3.0: docopt function returns a dict.
Isn’t it awesome how optparse and argparse generate help and usage-messages based on your code?!
Hell no! You know what’s awesome? It’s when the option parser is generated based on the beautiful usage-message that you write in a docstring! This way you don’t need to write this stupid repeatable parser-code, and instead can write only the usage-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 Mored (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 docstring above, that you pass to docopt function. docopt parses the usage-pattern ("Usage: ...") and option-descriptions (lines starting with dash -) and ensures that program invocation matches the ussage-pattern; it parses options, arguments and commands based on that. The basic idea is that a good usage-message has all necessary information in it to make a parser.
Even pep257 recommends putting usage-message in the module docstrings.
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.
from docopt import docopt
docopt takes 1 required and 3 optional arguments:
doc should be a module docstring (__doc__) or some other string that describes usage-message in a human-readable format, that will be parsed to create the option parser. The simple rules of how to write such a docstring 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 optional argument vector; by default it is the argument vector passed to your program (sys.argv[1:]). You can supply it with 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 usage-message (supplied as doc) and terminate, in case -h or --help options are encountered. If you want to handle -h or --help options manually (as all other options), set help=False.
version, by default None, is an optional argument that specifies the version of your program. If supplied, then, if parser encounters --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 doc. Also for your users to know about them.
The return value is just dictionary with options, arguments and commands, with keys spelled exactly like in usage-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 options, and args['move'] is a command.
Usage-message consists of 2 parts:
Usage-pattern, e.g.:
Usage: my_program.py [-hso FILE] [--quiet | --verbose] [INPUT ...]
Option-description, 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 our beautiful examples.
Usage-pattern is a substring of doc that starts with usage: (case-insensitive) and ends with 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 following elements:
Use the following operators to specify patterns:
If your usage-patterns allow to match same-named argument several times, parser will put matched values into a list, e.g. in case pattern is my-program.py FILE FILE then args['FILE'] will be a list; in case pattern is my-program.py FILE... it will also be a list.
Options-description is a list of options that you put below your ussage-patterns. It is required to list all options that are in ussage-patterns, their short/long versions (if any), and default values (if any).
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. 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: ./]
docopt lives on github.
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.
We think docopt is so good, we want to share it beyound the Python community!
Help developing Ruby port, or create port for your favorite language! You are encouraged to use Python version as reference implementation. Language-agnostic test-suite is on it’s way to be developed.
Porting discussion is on issues page.
docopt follows semantic versioning. 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==0.3.0