Correct documented exception in StateVectorMixin

cirq-core/cirq/sim/state_vector.py

@@ -135,8 +135,7 @@ def density_matrix_of(self, qubits: list[cirq.Qid] | None = None) -> np.ndarray:
 
         Raises:
             ValueError: if the size of the state represents more than 25 qubits.
-            IndexError: if the indices are out of range for the number of qubits
-                corresponding to the state.
+            KeyError: if some of the qubits provided are not in the quantum state.
         """
         return qis.density_matrix_from_state_vector(
             self.state_vector(),
@@ -160,8 +159,7 @@ def bloch_vector_of(self, qubit: cirq.Qid) -> np.ndarray:
 
         Raises:
             ValueError: if the size of the state represents more than 25 qubits.
-            IndexError: if index is out of range for the number of qubits
-                corresponding to the state.
+            KeyError: if the specified qubit is not in the quantum state.
         """
         return qis.bloch_vector_from_state_vector(
             self.state_vector(), self.qubit_map[qubit], qid_shape=self._qid_shape

cirq-core/cirq/sim/state_vector_test.py

@@ -405,6 +405,8 @@ def test_step_result_bloch_vector():
     bloch0 = np.array([0, 0, 1])
     np.testing.assert_array_almost_equal(bloch1, step_result.bloch_vector_of(q1))
     np.testing.assert_array_almost_equal(bloch0, step_result.bloch_vector_of(q0))
+    with pytest.raises(KeyError):
+        step_result.bloch_vector_of(cirq.LineQubit(2))
 
 
 def test_factor_validation():

examples/direct_fidelity_estimation.py

@@ -152,7 +152,7 @@ def _enumerate_all_from_stabilizer_bases(
 
 @dataclass
 class PauliTrace:
-    """Holder of a description fo Pauli states.
+    """Holder of a description of Pauli states.
 
     This class contains the Pauli states as described on page 2 of: https://arxiv.org/abs/1104.3835
     """