def gcd(a, b):
  
'''Return the greatest common divisor of a and b.'''
  a = abs(a)
  b = abs(b)
  if a < b:
    a, b = b, a
  while b != 0:
    a, b = b, a % b
  return a

def gcd(a: int, b: int) -> int:

>>> gcd.__annotations__
{'return': <class 'int'>, 'b': <class 'int'>, 'a': <class 'int'>}
>>> gcd.__annotations__['a']
<class 'int'>

def typecheck(f):
  def wrapper(*args, **kwargs):
    result = f(*args, **kwargs)
    return_type = f.__annotations__.get('return', None)
    if return_type and not isinstance(result, return_type):
      raise RuntimeError("{} should return {}".format(f.__name__, return_type.__name__))
    return result
  return wrapper

 
Traceback (most recent call last):
 File "typechecker.py", line 9, in <module>
  gcd(1, 2)
 File "typechecker.py", line 5, in wrapper
  raise RuntimeError("{} should return {}".format(f.__name__, return_type.__name__))
RuntimeError: gcd should return int

def typecheck(f):
  def wrapper(*args, **kwargs):
    for i, arg in enumerate(args[:f.__code__.co_nlocals]):
      name = f.__code__.co_varnames[i]
      expected_type = f.__annotations__.get(name, None)
      if expected_type and not isinstance(arg, expected_type):
        raise RuntimeError("{} should be of type {}; {} specified".format(name, expected_type.__name__, type(arg).__name__))
    result = f(*args, **kwargs)
    return_type = f.__annotations__.get('return', None)
    if return_type and not isinstance(result, return_type):
      raise RuntimeError("{} should return {}".format(f.__name__, return_type.__name__))
    return result
  return wrapper

for name, arg in kwargs.items():
  expected_type = f.__annotations__.get(name, None)
  if expected_type and not isinstance(arg, expected_type):
    raise RuntimeError("{} should be of type {}; {} specified".format(name, expected_type.__name__, type(arg).__name__))

def typecheck(f):
  def wrapper(*args, **kwargs):
    for i, arg in enumerate(args[:f.__code__.co_nlocals]):
      name = f.__code__.co_varnames[i]
      expected_type = f.__annotations__.get(name, None)
      if expected_type and not isinstance(arg, expected_type):
        raise RuntimeError("{} should be of type {}; {} specified".format(name, expected_type.__name__, type(arg).__name__))
    for name, arg in kwargs.items():
      expected_type = f.__annotations__.get(name, None)
      if expected_type and not isinstance(arg, expected_type):
        raise RuntimeError("{} should be of type {}; {} specified".format(name, expected_type.__name__, type(arg).__name__))
    result = f(*args, **kwargs)
    return_type = f.__annotations__.get('return', None)
    if return_type and not isinstance(result, return_type):
      raise RuntimeError("{} should return {}".format(f.__name__, return_type.__name__))
    return result
  return wrapper

def typecheck(f):
  def do_typecheck(name, arg):
    expected_type = f.__annotations__.get(name, None)
    if expected_type and not isinstance(arg, expected_type):
      raise RuntimeError("{} should be of type {} instead of {}".format(name, expected_type.__name__, type(arg).__name__))
 
  @functools.wraps(f)
  def wrapper(*args, **kwargs):
    for i, arg in enumerate(args[:f.__code__.co_nlocals]):
      do_typecheck(f.__code__.co_varnames[i], arg)
    for name, arg in kwargs.items():
      do_typecheck(name, arg)
 
    result = f(*args, **kwargs)
 
    do_typecheck('return', result)
    return result
  return wrapper