Decorator to check method param types. This solution give possibility to check method param type, raise needed exception type, and also have good readability in the decorator definition.

checktype

def accepts(exception,**types):
    def check_accepts(f):
        assert len(types) == f.func_code.co_argcount, \
        'accept number of arguments not equal with function number of arguments in "%s"' % f.func_name
        def new_f(*args, **kwds):
            for i,v in enumerate(args):
                if types.has_key(f.func_code.co_varnames[i]) and \
                    not isinstance(v, types[f.func_code.co_varnames[i]]):
                    raise exception("arg '%s'=%r does not match %s" % \
                        (f.func_code.co_varnames[i],v,types[f.func_code.co_varnames[i]]))
                    del types[f.func_code.co_varnames[i]]

            for k,v in kwds.iteritems():
                if types.has_key(k) and not isinstance(v, types[k]):
                    raise exception("arg '%s'=%r does not match %s" % \
                        (k,v,types[k]))

            return f(*args, **kwds)
        new_f.func_name = f.func_name
        return new_f
    return check_accepts


def exmaple():

    @accepts(Exception,a=int,b=list,c=(str,unicode))
    def test(a,b=None,c=None)
        print 'ok'

    test(13,c=[],b='df')