<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def is_contiguous(self):
        '''Return whether entire collection is contiguous.'''
        previous = None
        for index in self.indexes:
            if previous is None:
                previous = index
                continue

            if index != (previous + 1):
                return False

            previous = index

        return True