<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def viewbox(self):
 """ Return bounding box of the viewport. :return: (left, top, right, bottom) `tuple`. """

        return self.left, self.top, self.right, self.bottom