<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def replace(self, year=None, week=None):
 """Return a Week with either the year or week attribute value replaced"""

        return self.__class__(self.year if year is None else year,
                              self.week if week is None else week)