class_docstr: Affine warp constraints class.
  
  `AffineWarpConstraints` allow for
  very succinct definitions of constraints on
  the values of entries in affine transform matrices.
code: def num_dim(self):
      return self._num_dim
  
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 5 for calling the AffineWarpConstraints obj's underlying member method code with example usage: obj.num_dim() and returns: self