code: def test_compute_pi_stack(self):
      # order of the molecules shouldn't matter
      dicts1 = compute_pi_stack(self.prot, self.lig)
      dicts2 = compute_pi_stack(self.lig, self.prot)
      for i, j in ((0, 2), (1, 3)):
          self.assertEqual(dicts1[i], dicts2[j])
          self.assertEqual(dicts1[j], dicts2[i])
  
      # with this criteria we should find both types of stacking
      for d in compute_pi_stack(
          self.lig, self.prot, dist_cutoff=7, angle_cutoff=40.0
      ):
          self.assertGreater(len(d), 0)
  
imports: import os
  import unittest
  import numpy
  from deepchem.utils.rdkit_utils import load_molecule
  from deepchem.utils.rdkit_utils import compute_ring_center
  from deepchem.utils.rdkit_utils import compute_ring_normal
  from deepchem.utils.noncovalent_utils import is_pi_parallel
  from deepchem.utils.noncovalent_utils import is_pi_t
  from deepchem.utils.noncovalent_utils import compute_pi_stack
  from deepchem.utils.noncovalent_utils import is_cation_pi
  from deepchem.utils.noncovalent_utils import compute_cation_pi
  from deepchem.utils.noncovalent_utils import compute_binding_pocket_cation_pi
label_desc: Use image node_id 6 for calling the TestPiInteractions obj's underlying member method code with example usage: obj.test_compute_pi_stack() without return types