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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 _inverse_permutation_indices(positions):
 """Like inverse_permutation, but also handles slices. Parameters positions : list of np.ndarray or slice objects. If slice objects, all are assumed to be slices. Returns ------- np.ndarray of indices or None, if no permutation is necessary. """

    if not positions:
        return None

    if isinstance(positions[0], slice):
        positions = _consolidate_slices(positions)
        if positions == slice(None):
            return None
        positions = [np.arange(sl.start, sl.stop, sl.step) for sl in positions]

    indices = nputils.inverse_permutation(np.concatenate(positions))
    return indices