Fix NodeIndex.remove bug which misinterprets non-runnable patterns

Nodes were not removed from `NodeIndex` dictionary which allow
non-runnable patterns to use wrong nodes by mistake.

Related to TeamGraphix#193 (runnability issues).

graphix/sim/base_backend.py

@@ -77,6 +77,7 @@ def remove(self, node: int) -> None:
  """Remove the specified node label from the list and dictionary, and re-attributes qubit indices for the remaining nodes."""
  index = self.__dict[node]
  del self.__list[index]
+ del self.__dict[node]
  for new_index, node in enumerate(self.__list[index:], start=index):
  self.__dict[node] = new_index
 

tests/test_pattern.py

@@ -710,6 +710,13 @@ def test_arbitrary_inputs_tn(self, fx_rng: Generator, nqb: int, rand_circ: Circu
  backend="tensornetwork", graph_prep="sequential", input_state=states, rng=fx_rng
  )
 
+ def test_remove_qubit(self) -> None:
+ p = Pattern(input_nodes=[0, 1])
+ p.add(M(node=0))
+ p.add(C(node=0, clifford=clifford.X))
+ with pytest.raises(KeyError):
+ p.simulate_pattern()
+
 
 def assert_equal_edge(edge: Sequence[int], ref: Sequence[int]) -> bool:
  return any(all(ei == ri for ei, ri in zip(edge, other)) for other in (ref, reversed(ref)))