Decorate a function to automatically convert specified arguments from strings to datetimes

parse_dates.py

"""
Decorator to convert string arguments into datetimes automatically.
The decorated function will also still accept datetime objects per normal.
Useful for commandline tools, for example.

import dateutil.parser
import datetime
@parse_dates('start', 'some_date')
def days_until(some_date, start=None):
    if start_time is None:
        start_time = datetime.datetime.now()
    delta = end_time - start_time
    return delta.days

>>> christmas = dateutil.parser.parse('12/25')
>>> days_until(christmas, '12/20')
5

"""

import dateutil.parser
import inspect
import functools


def parse_dates(*argnames):
    def decorator(func):
        sig = inspect.signature(func)

        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            ba = sig.bind(*args, **kwargs)
            for argname in argnames:
                if argname in ba.arguments and isinstance(ba.arguments[argname], str):
                    ba.arguments[argname] = dateutil.parser.parse(ba.arguments[argname])
            return func(*ba.args, **ba.kwargs)

        return wrapper
    return decorator