type-docopt 0.8.2

Pythonic argument parser, with type description.

Type-Docopt: Pythonic argument parser, with type description

type-docopt helps you create beautiful command-line interfaces with type conversion:

"""Quick Example.

Usage:
  example.py transport <host> <port> [--timeout=<seconds>] [--protocol=<protocol>]
  example.py serial <port> [--baud=<n>] [--timeout=<seconds>]
  example.py (-h | --help | --version)

Options:
  -h, --help  Show this screen and exit.
  --baud=<n>  Baudrate [default: 9600] [type: int]
  --timeout=<seconds>  Timeout seconds [type: float]
  --protocol=<protocol>  Transport protocol [choices: tcp udp]
"""
from type_docopt import docopt

if __name__ == '__main__':
    arguments = docopt(__doc__)
    print(arguments)

$ python example.py transport 1.2.3.4 80 --timeout 0.5 --protocol tcp

{'--baud': 9600,
 '--help': False,
 '--protocol': 'tcp',
 '--timeout': 0.5,
 '--version': False,
 '<host>': '1.2.3.4',
 '<port>': '80',
 'serial': False,
 'transport': True}

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.

type-docopt project is based on docopt. docopt is a great project, but it lacks an important feature: type validation. It intensionally refuses to adding argument validation feature (For one example, refer to docopt#327). Furthermore, docopt seems not maintained anymore. type-docopt is a simple extension to docopt which adds type validation and conversion feature.

Installation

With pip or easy_install:

pip install type-docopt

type-docopt is tested on Python 3.6+.

Testing

You can run unit tests using the command:

python setup.py test

API

from type_docopt import docopt

docopt(docstring=None, argv=None, help_message=True, version=None, options_first=False, types=None)

docopt takes 6 optional arguments:

• docstring could be a module docstring (__doc__) or some other string that contains a help message that will be parsed to create the option parser. If it is None (not provided) - the calling scope will be interrogated for a docstring. 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 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'].

• help_message, 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_message=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.

• types, by default None, is how you can provide custom types to type-docopt. If given as a dictionary with type names as keys and type constructors as values, type-docopt converts argument values to given type according to the type information of option description. Basic types (int, float, complex, str) are readily available.

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. Dashes (-) between words are automatically converted to underscore (_). For example, if you invoke the top example as:

python example.py transport 1.2.3.4 80 --timeout 0.5 --protocol tcp

the return dictionary will be:

{'--baud': 9600,
 '--help': False,
 '--protocol': 'tcp',
 '--timeout': 0.5,
 '--version': False,
 '<host>': '1.2.3.4',
 '<port>': '80',
 'serial': False,
 'transport': True}

...and properties can be accessed with arguments.protocol or arguments.host.

Help message format

Help message consists of 2 parts:

• Usage pattern, e.g.:

  Usage: my_program.py [-hsc COUNT] [--quiet | --verbose] [INPUT ...]
  

• Option descriptions, e.g.:

  -h --help    show this
  -s --sorted  sorted output
  -c COUNT     specify count number [default: 1] [type: int]
  --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]
  

• If you would like to set type information for an option with an argument, put it into the option-description, in form [type: <my-type-name>]. You can also use default value with type description:

  --coefficient=K  The K coefficient [default: 2.95] [type: float]
  --count=COUNT    Count number [type: int]
  

• You can provide custom types to type-docopt. Make a dictionary with type names as keys and constructors as values then give it to type-docopt. Below is how you can convert file path to Path object.

  """Usage: my_program.py --output=FILE
  
  Options:
    --output=FILE  Output path [type: path]
  """
  from type_docopt import docopt
  from pathlib import Path
  
  if __name__ == '__main__':
      arguments = docopt(__doc__, types={'path': Path})
      print(arguments)
  

• If you want to specify allowable values for the argument, you can put the information into the option-description, in form [choices: <1st-choice> <2nd-choice> <3rd-choice>]. Choices are deliminated by whitespace. You can also use type and default value with choices:

  --protocol=PROTOCOL  Protocol name [choices: tcp udp] [default: tcp]
  --repeat=N           Number [choices: 1 2 3] [type: int]
  

Examples

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

Development

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

Make pull requests, report bugs, suggest ideas and discuss type-docopt.