Add __len__ to Schedule in Pulse along with related tests. (Qiskit#4394)

* Add __len__ to Schedule in Pulse along with its related tests (Qiskit#4171)

* Update __len__ in Pulse Schedule (Qiskit#4171)

* Update function name to test __len__ of Schedule in Pulse (Qiskit#4171)

Co-authored-by: Thomas Alexander <thomasalexander2718@gmail.com>

Co-authored-by: Thomas Alexander <thomasalexander2718@gmail.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit/pulse/schedule.py

@@ -555,6 +555,10 @@ def __lshift__(self, time: int) -> 'Schedule':
         """Return a new schedule which is shifted forward by ``time``."""
         return self.shift(time)
 
+    def __len__(self) -> int:
+        """Return number of instructions in the schedule."""
+        return len(self.instructions)
+
     def __repr__(self):
         name = format(self._name) if self._name else ""
         instructions = ", ".join([repr(instr) for instr in self.instructions[:50]])

test/python/pulse/test_schedule.py

@@ -186,9 +186,11 @@ def test_empty_schedule(self):
         self.assertEqual(0, sched.start_time)
         self.assertEqual(0, sched.stop_time)
         self.assertEqual(0, sched.duration)
+        self.assertEqual(0, len(sched))
         self.assertEqual((), sched._children)
         self.assertEqual({}, sched.timeslots)
         self.assertEqual([], list(sched.instructions))
+        self.assertFalse(sched)
 
     def test_overlapping_schedules(self):
         """Test overlapping schedules."""
@@ -530,6 +532,16 @@ def test_timeslots(self):
         self.assertEqual(
             reference_sched.timeslots[DriveChannel(1)], [(10, 60), (100, 100)])
 
+    def test_len(self):
+        """Test __len__ method"""
+        sched = Schedule()
+        self.assertEqual(len(sched), 0)
+
+        lp0 = self.linear(duration=3, slope=0.2, intercept=0.1)
+        for j in range(1, 10):
+            sched = sched.append(Play(lp0, self.config.drive(0)))
+            self.assertEqual(len(sched), j)
+
 
 class TestDelay(BaseTestSchedule):
     """Test Delay Instruction"""