Add queue size and __len__ methods (#2432)

python/ray/experimental/queue.py

@@ -27,10 +27,17 @@ class Queue(object):
         self.maxsize = maxsize
         self.actor = _QueueActor.remote(maxsize)
 
-    def qsize(self):
+    def __len__(self):
+        return self.size()
+
+    def size(self):
         """The size of the queue."""
         return ray.get(self.actor.qsize.remote())
 
+    def qsize(self):
+        """The size of the queue."""
+        return self.size()
+
     def empty(self):
         """Whether the queue is empty."""
         return ray.get(self.actor.qsize.remote())