Python check arguments types

def accepts(*argstypes, **kwargstypes):
    def wrapper(func):
        def wrapped(*args, **kwargs):
            if len(args) > len(argstypes):
                raise TypeError("%s() takes at most %s non-keyword arguments (%s given)" % (func.__name__, len(argstypes), len(args)))
            argspairs = zip(args, argstypes)
            for k,v in kwargs.items():
                if k not in kwargstypes:
                    raise TypeError("Unexpected keyword argument '%s' for %s()" % (k, func.__name__))
                argspairs.append((v, kwargstypes[k]))
            for param, expected in argspairs:
                if param is not None and not isinstance(param, expected):
                    raise TypeError("Parameter '%s' is not %s" % (param, expected.__name__))
            return func(*args, **kwargs)
        return wrapped
    return wrapper

>>> @accepts(str, arg2=int)
... def f(arg1, arg2=None):
...     pass
...

>>> f('foo')
>>> f('foo', arg2=3)
>>> f()
TypeError: f() takes at least 1 argument (0 given)
>>> f('foo', 'bar')
TypeError: f() takes at most 1 non-keyword arguments (2 given)
>>> f('foo', arg2='bar')
TypeError: Parameter 'bar' is not int
>>> f('foo', arg3='bar')
TypeError: Unexpected keyword argument 'arg3' for f()

>>> class A(object):
...     pass
...
>>> class B(object):
...     @accepts(object, (str, unicode))
...     def f(self, s):
...         pass
...
...     @accepts(object, A)
...     def g(self, a):
...         pass

>>>
>>> b = B()
>>> b.f(u'foo')
>>> b.f('foo')
>>> b.g(A())
>>> b.g(B())
TypeError: Parameter '<__main__.B object at 0x902466c>' is not A

def returns(rtype):
    def wrapper(f):
        def wrapped(*args, **kwargs):
            result = f(*args, **kwargs)
            if not isinstance(result, rtype):
                raise TypeError("return value %r does not match %s" % (result,rtype))
            return result
        return wrapped
    return wrapper

>>> @accepts(str, arg2=int)
... @returns(int)
... def f(arg1, arg2=None):
...     return 0
...