class_docstr: Affine warp constraints class.
  
  `AffineWarpConstraints` allow for
  very succinct definitions of constraints on
  the values of entries in affine transform matrices.
docstr: Assign constraints on translation components of
  affine transform in 3d.
docstr_tok: ["Assign","constraints","on","translation","components","of","affine","transform","in","3d","."]
code: def translation_3d(cls, x=None, y=None, z=None):
      """
      Assign constraints on translation components of
      affine transform in 3d.
      """
      return cls(
          [
              [None, None, None, x],
              [None, None, None, y],
              [None, None, None, z],
          ]
      )
  
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 12 for calling the AffineWarpConstraints obj's underlying member method code with example usage: obj.translation_3d(cls, x, y, z) and returns: cls