'Pop the frame at the top of the stack.
@return: The popped frame, else None.
@rtype: L{Frame}'

def pop(self):

    if len(self.stack):
        popped = self.stack.pop()
        log.debug('pop:    (%s)\n%s', Repr(popped), Repr(self.stack))
        return popped
    else:
        log.debug('stack    empty,    not-popped')
    return None
