Enforce new python3.6 type decorators at runtime with this decorator.

enforce.py

#!/bin/env python

def enforce(func):
  ''' Decorator to enforce type decorators at runtime via
  type assertion. Usage:
  @enforce
  def foo(a : str, b : int, c = True : bool) -> str:
    return None
  '''
  def enforce_wrapper(*args, **kwargs):
    for k, v in dict(zip(func.__code__.co_varnames, args),
                     **dict(zip(func.__code__.co_varnames[len(args):func.__code__.co_argcount],
                                func.__defaults__) if func.__defaults__ else {},
                            **kwargs)).items():
      assert type(v) == func.__annotations__.get(k, type(v)), \
           "Argument `%s : %s` received type `%s`." % (
              k, func.__annotations__.get(k), type(v))
    ret = func(*args, **kwargs)
    assert type(ret) == func.__annotations__.get('return', type(ret)), \
           "`%s(...) -> %s` returned type `%s`." % (
              func.__name__, func.__annotations__.get('return'), type(ret)
            )
    return ret
  return enforce_wrapper

test_enforce.py

from enforce import enforce
from unittest import TestCase

@enforce
def test_1() -> bool:
  return None

@enforce
def test_2(a : str, b, c : bool = 0) -> str:
  return ''

class TestEnforce(TestCase):
  def test_return_error(self):
    with self.assertRaises(AssertionError):
      test_1()

  def test_no_error(self):
    test_2('a', 'b', False)

  def test_bad_arg(self):
    with self.assertRaises(AssertionError):
      test_2('a', 0, 0)

  def test_default_type_error(self):
    with self.assertRaises(AssertionError):
      test_2('a', 'b')