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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def n_frames_total(self, stride=1, skip=0):
 r"""Returns total number of frames. Parameters stride : int return value is the number of frames in trajectories when running through them with a step size of `stride`. skip : int, default=0 skip the first initial n frames per trajectory. Returns ------- n_frames_total : int total number of frames. """

        if not IteratorState.is_uniform_stride(stride):
            return len(stride)

        return sum(self.trajectory_lengths(stride=stride, skip=skip))