schema_validation.py

"""
Use functools to declare the specification of inputs and validate
them on the fly with decorator.

It also only currently works with keyword arguments only, just to keep
it simpler (and because enforcing them might be a good idea anyway).
"""

import functools
import voluptuous as V

MessageSchema = V.Schema({
    V.Required('to'): str,
    V.Required('preserve_recipients'): bool,
})


class InvalidField(Exception):
    pass


class validate_input(object):
    def __init__(self, **validators):
        self.validators = validators

    def __call__(self, func):
        @functools.wraps(func)
        def _wrapped(**kwargs):
            new_kwargs = {}
            for key, value in kwargs.items():
                try:
                    new_value = self.validators[key](value)
                except V.Invalid as e:
                    raise InvalidField("Could not validate field %s, voluptuous error: %s" % (key, e.errors))
                else:
                    new_kwargs[key] = new_value

            return func(**new_kwargs)

        return _wrapped


@validate_input(message=MessageSchema)
def my_function(message):
    print(message)


if __name__ == '__main__':
    # working case
    my_function(message={'to': 'hello@world', 'preserve_recipients': True})

    # mismatching type
    my_function(message={'to': 'hello@world', 'preserve_recipients': 'true'})

    # missing required
    my_function(message={'preserve_recipients': 'true'})