<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add_url(self, *args, **kwargs):
 """Add a new url to the sitemap. This function can either be called with a :class:`UrlEntry` or some keyword and positional arguments that are forwarded to the :class:`UrlEntry` constructor. """

        if len(args) == 1 and not kwargs and isinstance(args[0], UrlEntry):
            self.urls.append(args[0])
        else:
            self.urls.append(UrlEntry(*args, **kwargs))