Sunday, December 8, 2013

Docopt is amazing

I love the command line and I love Python. So, naturally, I am an avid user of the argparse module bundled with Python. Today I discovered docopt and I am so totally converted. argparse is great but there is a bunch of setup code that you have to write and often things look very boilerplate-y and messy and it just looks like there should be a more concise way of expressing the command line interface to a program. Enter docopt

docopt allows you to describe your commandline interface in your doc string and then it parses this description and creates a command line parser that returns a dictionary with the values for all the options filled in. Just like that.

So, for example, one of my scripts has a docstring that looks like

Usage:
  compute_eye_epoch [-R DATAROOT] [-x EXCEL] [-d DATABASE] [-e EPOCH] [-f|-F] [-q]

Options:
  -h --help     Show this screen and exit.
  -R DATAROOT   Root of data directory [default: ../../Data]
  -x EXCEL      Spreadsheet with sessions/trials etc [default: ../../Notes/sessions_and_neurons.xlsx]
  -d DATABASE   sqlite3 database we write to [default: test.sqlite3]
  -e EPOCH      Name of epoch we want to process
  -f            Force recomputation of all entries for this epoch
  -F            Force storing of epoch (automatically forces recomputation)
  -q            Quiet mode (print only ERROR level logger messages)

And the __main__ part of the code is

import docopt

if __name__ == '__main__':
  arguments = docopt.docopt(__doc__, version='v1')
  print arguments

If I call the program with -h then I get the usage information printed and the program exits. If I call it with other options args will be filled out, for example:

{'-F': False,
 '-R': '../../Data',
 '-d': 'test.sqlite3',
 '-e': None,
 '-f': False,
 '-q': False,
 '-x': '../../Notes/sessions_and_neurons.xlsx'}

This totally removes the barrier to creating command line interfaces and removes clutter from the __main__ section of the code! Amazing! Give it a try!

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