def diff_frames(self, prev):
    if (len(self.frames) != len(prev.frames)):
        return None
    updated = []
    for i in range(len(self.frames)):
        f = self.frames[i]
        prev_f = prev.frames[i]
        if (f.location_context == prev_f.location_context):
            if f.is_different(prev_f):
                updated.append(i)
        else:
            return None
    return updated
def diff_frames(self, prev):
    if (len(self.frames) != len(prev.frames)):
        return None
    updated = []
    for i in range(len(self.frames)):
        f = self.frames[i]
        prev_f = prev.frames[i]
        if (f.location_context == prev_f.location_context):
            if f.is_different(prev_f):
                updated.append(i)
        else:
            return None
    return updated