python decorator to make functions act statically typed

gistfile1.py

function = type(lambda x: x)

def __listcheck(typ, arg):
    for i,x in enumerate(arg):
        if not any((_typecheck(t, x) for t in typ)):
            raise TypeError, "List member %s, \"%s\" is not of type %s!"%(i,x,typ)
    return True

def __tuplecheck(typ, arg):
    if len(typ) != len(arg):
        raise TypeError, "Tuple length did not match."
    for t,a,i in zip(typ, arg, range(len(typ))):
        if not _typecheck(t, a):
            raise TypeError, "Tuple member %s, \"%s\" is not of type %s!"%(i,a,t)
    return True

def __setcheck(typ, arg):
    for x in arg:
        if not any((_typecheck(t, x) for t in typ)):
            raise TypeError, "Set member \"%s\" is not of type %s!"%(x, typ)
    return True

def __frozensetcheck(typ, arg):
    for x in arg:
        if not any((_typecheck(t, x) for t in typ)):
            raise TypeError, "Frozenset member \"%s\" is not of type %s!"%(x, typ)
    return True

def __dictcheck(typ, arg):
    for k,v in arg.iteritems():
        for ktyp, vtyp in typ.iteritems():
            if _typecheck(ktyp, k) and _typecheck(vtyp, v):
                break
        else:
            raise TypeError, "Dictionary member \"%s:%s\" is not of type %s!" % (k,v,typ)
    return True

_deepchecks = {
        list:       __listcheck,
        tuple:      __tuplecheck,
        set:        __setcheck,
        frozenset:  __frozensetcheck,
        dict:       __dictcheck,
    }

def _typecheck(typ, arg):
    if isinstance(typ, type):
        if not isinstance(arg, typ):
            return False
    elif isinstance(typ, function) and not typ(arg):
        return False
    elif not isinstance(arg, type(typ)):
        return False
    if type(arg) in _deepchecks:
        if not _deepchecks[type(arg)](typ, arg):
            return False
    return True

def typed(*types, **kwtypes):
    def outerwrapper(func):
        def wrapper(*args, **kwargs):
            if len(args) != len(types):
                raise TypeError, "Incorrect argument count."
            for typ, arg in zip(types, args):
                if not _typecheck(typ, arg):
                    raise TypeError, "Argument %s failed typecheck." % (arg)
            for kw, arg in kwargs.iteritems():
                vtype = kwtypes.get(kw, None)
                if vtype is None:
                    raise TypeError, "Encountered unexpected keyword argumement %s."%kw
                _typecheck(vtype, arg)
            return func(*args, **kwargs)
        return wrapper
    return outerwrapper

@typed(lambda x: x)
def identity(x):
    print x

@typed([int])
def test(x):
    print x

@typed((int, str))
def tupletest(tup):
    print tup

@typed({int: int})
def intmap(d):
    print d

@typed(int, a=str, b=int)
def opt(i, a=None, b=None):
    print i, a, b