code: def _unitary(norm):
      if norm not in (None, "ortho", "no_norm"):
          raise ValueError(
              "Invalid value %s for norm, must be None, 'ortho' or "
              "'no norm'" % norm
          )
      return norm
  
imports: from __future__ import absolute_import, print_function, division
  import numpy
  from theano import gof
  import theano.tensor
  from theano.gradient import DisconnectedType
label_desc: Use image node_id 3 for calling a global function with example usage: _unitary(norm) and returns: norm