validation_example.py

"""Usage: prog.py [--count=N] PATH FILE...

Arguments:
  FILE     input file
  PATH     out directory

Options:
  --count=N   number of operations

"""
import os

from docopt import docopt
try:
    from schema import Schema, And, Or, Use, SchemaError
except ImportError:
    exit('This example requires that `schema` data-validation library'
         ' is installed: \n    pip install schema\n'
         'https://github.com/halst/schema')


if __name__ == '__main__':
    args = docopt(__doc__)

    schema = Schema({
        'FILE': [Use(open, error='FILE should be readable')],
        'PATH': And(os.path.exists, error='PATH should exist'),
        '--count': Or(None, And(Use(int), lambda n: 0 < n < 5),
                      error='--count=N should be integer 0 < N < 5')})
    try:
        args = schema.validate(args)
    except SchemaError as e:
        exit(e)

    print(args)