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docopt overview

  • Created by Vladimir Keleshev

  • PyCon UK video - docopt intro

  • Some code snippets taken from above site

Command line tools

  • API for your program

  • Often act as a base design for developing UI

  • A well defined command line program makes you program against an interface and not an implementation

  • Sample command line: usage.txt

Parsing command line using optparse

  • Not much support beyond adding options (the -- stuff)

  • Need to write logic for subcommands

  • A series of if-this-sub_command-validate-sub_command-env statements

  • Program: connector_1.py

Parsing command line using argparse

  • More intuitive than optparse

  • Can add subparsers (sub_commands)

  • Creates help usage on the fly (try doing program sub_command help)

  • Was using this before docopt found me

  • Have tried only optparse, argparse and docopt. Any other favorite command line parsers?

  • Program: connector_2.py

Parsing command line using docopt

  • Specify a POSIX complaint usage (more fun than it sounds)

  • Write your doc first

  • docopt takes care of the rest

  • Sort of like specifying a syntax and try to fit your command line in it

  • No semantic validation (e.g. is --src_file a valid file?)

    • a good thing - I would rather employ my own mechanisms (more later)
  • Program: connector_3.py

Keep the design and development separate

  • Read man page of git command

  • Copied the synopsis, made minimal changes and added functionality to support git and git add command in less than 10 minutes.

  • Keep the command line parsing work as minimal as possible

  • Break it into chunks - syntactic validation, semantic validation so that both can be done separately

  • Try writing that with argparse

  • Mind. Blown.

  • Program: git_1.py

Validating the input

  • Use schema module

  • I find the separation of parsing and validating natural and intuitive.

  • Program: rule_filter.py

Handy docopt options

  • Supports a lot of interesting features e.g. specifying command line switch multiple times, mandating usage of arguments in pairs, etc.

  • Program: one_liners.py

  • See module documentation for an exhaustive list

Wrapping up