Loader: clean up callback awaiter code via Python 3.6+ syntax

direct/src/showbase/Loader.py

@@ -31,42 +31,6 @@ class Loader(DirectObject):
         # This indicates that this class behaves like a Future.
         _asyncio_future_blocking = False
 
-        class _ResultAwaiter(object):
-            """Reinvents generators because of PEP 479, sigh.  See #513."""
-
-            __slots__ = 'requestList', 'index'
-
-            def __init__(self, requestList):
-                self.requestList = requestList
-                self.index = 0
-
-            def __await__(self):
-                return self
-
-            def __anext__(self):
-                if self.index >= len(self.requestList):
-                    raise StopAsyncIteration
-                return self
-
-            def __iter__(self):
-                return self
-
-            def __next__(self):
-                i = self.index
-                request = self.requestList[i]
-                if not request.done():
-                    return request
-
-                self.index = i + 1
-
-                result = request.result()
-                if isinstance(result, PandaNode):
-                    result = NodePath(result)
-
-                exc = StopIteration(result)
-                exc.value = result
-                raise exc
-
         def __init__(self, loader, numObjects, gotList, callback, extraArgs):
             self._loader = loader
             self.objects = [None] * numObjects
@@ -124,13 +88,15 @@ class Loader(DirectObject):
 
             if self.requests:
                 self._asyncio_future_blocking = True
+                while self.requests:
+                    yield self
 
             if self.gotList:
-                return self._ResultAwaiter([self])
+                return self.objects
             else:
-                return self._ResultAwaiter(self.requestList)
+                return self.objects[0]
 
-        def __aiter__(self):
+        async def __aiter__(self):
             """ This allows using `async for` to iterate asynchronously over
             the results of this class.  It does guarantee to return the
             results in order, though, even though they may not be loaded in
@@ -138,7 +104,8 @@ class Loader(DirectObject):
             requestList = self.requestList
             assert requestList is not None, "Request was cancelled."
 
-            return self._ResultAwaiter(requestList)
+            for req in requestList:
+                yield await req
 
     # special methods
     def __init__(self, base):