type annotation validator

gistfile1.py

#!/usr/bin/env python
# -*- Mode: python; tab-width: 4; indent-tabs-mode: nil; coding: utf-8; -*-

import inspect
from functools import wraps


class AnnotationValidateError(Exception):
    pass


def validate(f):
    @wraps(f)
    def wrapper(*args, **kwarg):
        sig = inspect.signature(f)
        params = dict(zip(sig.parameters, args))
        for k, v in sig.parameters.items():
            if k in params:
                if not v.annotation(params[k]):
                    e = 'annotation type {}={}, but given {}'.format(k, v.name, type(params[k]))
                    raise AnnotationValidateError(e)
        ret = f(*args, **kwarg)
        if sig.return_annotation is not sig.empty:
            if type(ret) is not sig.return_annotation:
                e = 'annotation return type={}, but returned={}'.format(sig.return_annotation, type(ret))
                raise AnnotationValidateError(e)
        return ret
    return wrapper

def foo(x: int) -> str:
    return str(x)
print(foo(100))  # ok
print(foo('bar'))  # AnnotationValidateError