code: def test_diff_hamiltonian_active_space():
      r"""Test that diff_hamiltonian works when an active space is defined."""
  
      symbols = ["H", "H", "H"]
      geometry = np.array(
          [[0.0, 0.0, 0.0], [2.0, 0.0, 1.0], [0.0, 2.0, 0.0]]
      )
  
      mol = qchem.Molecule(symbols, geometry, charge=1)
      args = [geometry]
  
      h = qchem.diff_hamiltonian(mol, core=[0], active=[1, 2])(*args)
  
      assert isinstance(h, qml.Hamiltonian)
  
      enable_new_opmath()
      h_op = qchem.diff_hamiltonian(mol, core=[0], active=[1, 2])(*args)
      disable_new_opmath()
  
      assert not isinstance(h_op, qml.Hamiltonian)
  
file_path: pennylane/tests/qchem/test_hamiltonians.py
imports: import pytest
  import pennylane
  from pennylane import Identity, PauliX, PauliY, PauliZ
  from pennylane import numpy
  from pennylane import qchem
  from pennylane.operation import disable_new_opmath, enable_new_opmath
  from pennylane.fermi import from_string
label_desc: Use image node_id 4 for calling a global function with example usage: test_diff_hamiltonian_active_space() without return types