class_docstr: Affine warp constraints class.
  
  `AffineWarpConstraints` allow for
  very succinct definitions of constraints on
  the values of entries in affine transform matrices.
docstr: Assigns constraints on shear components of
  affine transform in 3d.
docstr_tok: ["Assigns","constraints","on","shear","components","of","affine","transform","in","3d","."]
code: def no_shear_3d(cls):
      """
      Assigns constraints on shear components of
      affine transform in 3d.
      """
      return cls(
          [[None, 0, 0, None], [0, None, 0, None], [0, 0, None, None]]
      )
  
imports: from __future__ import absolute_import, division, print_function
  from itertools import chain
  import numpy
  import tensorflow
  from niftynet.layer.base_layer import Layer, LayerFromCallable, Invertible
label_desc: Use image node_id 17 for calling the AffineWarpConstraints obj's underlying member method code with example usage: obj.no_shear_3d(cls) and returns: cls