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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 _ordered_idx_from_perm(self, perm_str):
 """Return the ordered index of ``perm_str`` or None if ``perm_str`` is not a valid permission."""

        for i, ordered_str in enumerate(ORDERED_PERM_LIST):
            if perm_str == ordered_str:
                return i