Decorator for enforcing strict type annotations on functions

strict_types.py

import typing
import inspect
import functools


def strict_types(func: typing.Callable):
    """Decorator for enforcing strict type annotations"""

    argspec = inspect.getfullargspec(func)
    ret_type = argspec.annotations.pop('return', None)

    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        for arg, cls in argspec.annotations.items():
            if arg in kwargs:
                val = kwargs.get(arg)
            else:
                try:
                    i = argspec.args.index(arg)
                    val = args[i]
                except ValueError:
                    continue

            if val is not None and not isinstance(val, cls):
                raise ValueError('Expected %r to be of type %r, '
                                 'but got %r instead' % (arg, cls.__name__,
                                                         val.__class__.__name__))

        ret_val = func(*args, **kwargs)
        if ret_type and ret_val is not None and not isinstance(ret_val, ret_type):
            raise ValueError('Expected return value to be of type %r, '
                             'but got %r instead' % (cls.__name__,
                                                     ret_val.__class__.__name__))

    return wrapper