Add __len__ method to Carrier (#614)

Author: rickwierenga

pylabrobot/resources/carrier.py

@@ -52,6 +52,10 @@ def capacity(self):
     """The number of sites on this carrier."""
     return len(self.sites)
 
+  def __len__(self) -> int:
+    """Return the number of sites on this carrier."""
+    return len(self.sites)
+
   def assign_child_resource(
     self,
     resource: Resource,

pylabrobot/resources/carrier_tests.py

@@ -160,6 +160,9 @@ def test_absolute_location(self):
   def test_capacity(self):
     self.assertEqual(self.tip_car.capacity, 5)
 
+  def test_len(self):
+    self.assertEqual(len(self.tip_car), 5)
+
   def test_assignment(self):
     self.tip_car[0] = self.A
     self.tip_car[1] = self.B