<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def page(self, number=None):
 """ If page is given, modify the URL correspondingly, return the current page otherwise. """

        if number is None:
            return int(self.url.page)
        self.url.page = str(number)