Fix/5015 QuantumCircuit __eq__ should always return a Bool

qiskit/circuit/quantumcircuit.py

@@ -220,6 +220,9 @@ def __str__(self):
         return str(self.draw(output='text'))
 
     def __eq__(self, other):
+        if not isinstance(other, QuantumCircuit):
+            return False
+
         # TODO: remove the DAG from this function
         from qiskit.converters import circuit_to_dag
         return circuit_to_dag(self) == circuit_to_dag(other)

test/python/circuit/test_circuit_operations.py

@@ -587,6 +587,38 @@ def test_inverse(self):
         expected.global_phase = -0.5
         self.assertEqual(qc.inverse(), expected)
 
+    def test_compare_two_equal_circuits(self):
+        """Test to compare that 2 circuits are equal.
+        """
+        qc1 = QuantumCircuit(2, 2)
+        qc1.h(0)
+
+        qc2 = QuantumCircuit(2, 2)
+        qc2.h(0)
+
+        self.assertTrue(qc1 == qc2)
+
+    def test_compare_two_different_circuits(self):
+        """Test to compare that 2 circuits are different.
+        """
+        qc1 = QuantumCircuit(2, 2)
+        qc1.h(0)
+
+        qc2 = QuantumCircuit(2, 2)
+        qc2.x(0)
+
+        self.assertFalse(qc1 == qc2)
+
+    def test_compare_a_circuit_with_none(self):
+        """Test to compare that a circuit is different to None.
+        """
+        qc1 = QuantumCircuit(2, 2)
+        qc1.h(0)
+
+        qc2 = None
+
+        self.assertFalse(qc1 == qc2)
+
 
 class TestCircuitBuilding(QiskitTestCase):
     """QuantumCircuit tests."""