Note
New in version 0.4.0:
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, pep257 recommends putting help 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 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 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 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:
Use the following constructs to specify patterns:
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 consist of a list of options that you put below your ussage patterns.
It is necessary to list option descriptions in order to specify:
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, 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 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.
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