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Video introduction todocopt:PyCon UK 2012: Create *beautiful*command-line interfaces with Python

New in version 0.6.1:

• Fix issue#85which caused improper handling of[options] shortcutif it was present several times.

New in version 0.6.0:

• New argumentoptions_first, disallows interspersing optionsand arguments. If you supplyoptions_first=True todocopt, it will interpret all arguments as positionalarguments after first positional argument.
• If option with argument could be repeated, its default valuewill 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. Previouslyit meant"any known option". Now it means"any option not inusage-pattern". This avoids the situation when an option isallowed to be repeated unintentionally.
• argv isNone by default, notsys.argv[1:].This allowsdocopt to always use thelatestsys.argv,notsys.argv during import time.

Isn't it awesome howoptparse andargparse generate helpmessages based on your code?!

Hell no! You know what's awesome? It's when the option parserisgenerated 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 interfaceseasily:

"""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 --versionOptions:  -h --help     Show this screen.  --version     Show version.  --speed=<kn>  Speed in knots [default: 10].  --moored      Moored (anchored) mine.  --drifting    Drifting mine."""fromdocoptimportdocoptif__name__=='__main__':arguments=docopt(__doc__,version='Naval Fate 2.0')print(arguments)

Beat that! The option parser is generated based on the docstring abovethat is passed todocopt function.docopt parses the usagepattern ("Usage: ...") and option descriptions (lines startingwith dash "-") and ensures that the program invocation matches theusage pattern; it parses options, arguments and commands based onthat. The basic idea is thata good help message has all necessaryinformation in it to make a parser.

Also,PEP 257 recommendsputting help message in the module docstrings.

Usepip or easy_install:

pip install docopt==0.6.2

Alternatively, you can just dropdocopt.py file into yourproject--it is self-contained.

docopt is tested with Python 2.7, 3.4, 3.5, and 3.6.

You can run unit tests using the command:

python setup.py test

fromdocoptimportdocopt

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 otherstring that contains ahelp message that will be parsed tocreate the option parser. The simple rules of how to write such ahelp message are given in next sections. Here is a quick example ofsuch 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 defaultdocopt usesthe argument vector passed to your program (sys.argv[1:]).Alternatively you can supply a list of strings like['--verbose','-o', 'hai.txt'].

• help, by defaultTrue, specifies whether the parser shouldautomatically print the help message (supplied asdoc) andterminate, in case-h or--help option is encountered(options should exist in usage pattern, more on that below). If youwant to handle-h or--help options manually (as otheroptions), sethelp=False.

• version, by defaultNone, is an optional argument thatspecifies the version of your program. If supplied, then, (assuming--version option is mentioned in usage pattern) when parserencounters the--version option, it will print the suppliedversion and terminate.version could be any printable object,but most likely a string, e.g."2.1.0rc1".

  Note, whendocopt is set to automatically handle-h,--help and--version options, you still need to mentionthem in usage pattern for this to work. Also, for your users toknow about them.

• options_first, by defaultFalse. If set toTrue willdisallow mixing options and positional argument. I.e. after firstpositional argument, all arguments will be interpreted as positionaleven if the look like options. This can be used for strictcompatibility with POSIX, or if you want to dispatch your argumentsto other programs.

Thereturn value is a simple dictionary with options, argumentsand commands as keys, spelled exactly like in your help message. Longversions of options are given priority. For example, if you invoke thetop 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'}

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 is a substring ofdoc that starts withusage: (caseinsensitive) and ends with avisibly empty line.Minimum example:

"""Usage: my_program.py"""

The first word afterusage: is interpreted as your program's name.You can specify your program's name several times to signify severalexclusive 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 eitherupper-case words, e.g.my_program.py CONTENT-PATH or wordssurrounded 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-letteroptions, e.g.-oiv which will be the same as-o -i -v. Theoptions can have arguments, e.g.--input=FILE or-i FILE oreven-iFILE. However it is important that you specify optiondescriptions if you want your option to have an argument, a defaultvalue, or specify synonymous short/long versions of the option (seenext section on option descriptions).
• commands are words that donot follow the described aboveconventions of--options or<arguments> orARGUMENTS,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 arenotput in[ ] are also required, e.g.:my_program.py--path=<path> <file>... is the same asmy_program.py(--path=<path> <file>...). (Note, "required options" might be nota 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. Groupthem using[ ] if none of the mutually-exclusive elements arerequired:my_program.py [--left | --right].
• ... (ellipsis)one or more elements. To specify thatarbitrary number of repeating elements could be accepted, useellipsis (...), e.g.my_program.py FILE ... means one ormoreFILE-s are accepted. If you want to accept zero or moreelements, use brackets, e.g.:my_program.py [FILE ...]. Ellipsisworks as a unary operator on the expression to the left.
• [options] (case sensitive) shortcut for any options. You canuse it if you want to specify that the usage pattern could beprovided with any options defined below in the option-descriptionsand do not want to enumerate them all in usage-pattern.
• "[--]". Double dash "--" is used by convention to separatepositional arguments that can be mistaken for options. In order tosupport this convention add "[--]" to your usage patterns.
• "[-]". Single dash "-" is used by convention to signify thatstdin 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) severaltimes:

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

then number of occurrences of the option will be counted. I.e.args['-v'] will be2 if program was invoked asmy_program-vv. Same works for commands.

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

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

I.e. invoked withmy_program.py file1 file2 --path=./here--path=./there the returned dict will containargs['<file>'] ==['file1', 'file2'] andargs['--path'] == ['./here', './there'].

Option descriptions consist of a list of options that you putbelow 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 indoc that starts with- or-- (not countingspaces) is treated as an option description, e.g.:

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

• To specify that option has an argument, put a word describing thatargument after space (or equals "=" sign) as shown below. Followeither <angular-brackets> or UPPER-CASE convention for options'arguments. You can use comma if you want to separate options. Inthe example below, both lines are valid, however you are recommendedto 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 itis repeatable, it will besplited 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]

We have an extensive list ofexamples which coverevery aspect of functionality ofdocopt. Try them out, read thesource if in doubt.

If you want to split your usage-pattern into several, implementmulti-level help (with separate help-screen for each subcommand),want to interface with existing scripts that don't usedocopt, oryou're building the next "git", you will need the newoptions_firstparameter (described in API section above). To get you started quicklywe implemented a subset of git command-line interface as an example:examples/git

docopt does one thing and does it well: it implements yourcommand-line interface. However it does not validate the input data.On the other hand there are libraries likepython schema which make validating data abreeze. Take a look atvalidation_example.pywhich usesschema to validate data and report an error to theuser.

Often configuration files are used to provide default values whichcould be overriden by command-line arguments. Sincedocoptreturns a simple dictionary it is very easy to integrate withconfig-files written in JSON, YAML or INI formats.config_file_example.py providesand example of how to usedocopt with JSON or INI config-file.

We wouldlove to hear what you think aboutdocopt on ourissuespage

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

We thinkdocopt is so good, we want to share it beyond the Pythoncommunity! All official docopt ports to other languages can be foundunder thedocopt organization pageon GitHub.

If your favourite language isn't among then, you can always create aport for it! You are encouraged to use the Python version as areference implementation. A Language-agnostic test suite is bundledwithPython implementation.

Porting discussion is onissues page.

docopt followssemantic versioning. Thefirst release with stable API will be 1.0.0 (soon). Until then, youare encouraged to specify explicitly the version in your dependencytools, e.g.:

pip install docopt==0.6.2

• 0.6.2 Bugfix release.
• 0.6.1 Bugfix release.
• 0.6.0options_first parameter.Breaking changes: Corrected[options] meaning.argv defaults toNone.
• 0.5.0 Repeated options/commands are counted or accumulated into alist.
• 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 onusage patterns.Breaking changes:docopt returns namespace (for arguments),not list. Usage pattern is formalized.
• 0.1.0 Initial release. Options-parsing only (based on optionsdescription).