code: def affine(self, i):
      aff = np.eye(4)
      aff[0:3, :] = self._affines[i].reshape(3, 4)
      return aff
  
file_path: nipy/nipy/algorithms/registration/polyaffine.py
imports: import numpy
  from ._registration import _apply_polyaffine
  from .affine import apply_affine
  from .transform import Transform
label_desc: Use image node_id 2 for calling the PolyAffine obj's underlying member method code with example usage: obj.affine(i) and returns: aff