refactor "yield from" and "await" nodes a little to provide a cleaner split...

refactor "yield from" and "await" nodes a little to provide a cleaner split between them (await nodes are not yield-from nodes)

Cython/Compiler/ExprNodes.py

@@ -9491,20 +9491,9 @@ class YieldExprNode(ExprNode):
             code.put_incref(self.result(), py_object_type)
 
 
-class YieldFromExprNode(YieldExprNode):
-    # "yield from GEN" expression
-    is_yield_from = True
-    expr_keyword = 'yield from'
-
-    def coerce_yield_argument(self, env):
-        if not self.arg.type.is_string:
-            # FIXME: support C arrays and C++ iterators?
-            error(self.pos, "yielding from non-Python object not supported")
-        self.arg = self.arg.coerce_to_pyobject(env)
-
+class _YieldDelegationExprNode(YieldExprNode):
     def yield_from_func(self, code):
-        code.globalstate.use_utility_code(UtilityCode.load_cached("GeneratorYieldFrom", "Coroutine.c"))
-        return "__Pyx_Generator_Yield_From"
+        raise NotImplementedError()
 
     def generate_evaluation_code(self, code, source_cname=None, decref_source=False):
         if source_cname is None:
@@ -9546,13 +9535,28 @@ class YieldFromExprNode(YieldExprNode):
         code.putln("}")
 
 
-class AwaitExprNode(YieldFromExprNode):
+class YieldFromExprNode(_YieldDelegationExprNode):
+    # "yield from GEN" expression
+    is_yield_from = True
+    expr_keyword = 'yield from'
+
+    def coerce_yield_argument(self, env):
+        if not self.arg.type.is_string:
+            # FIXME: support C arrays and C++ iterators?
+            error(self.pos, "yielding from non-Python object not supported")
+        self.arg = self.arg.coerce_to_pyobject(env)
+
+    def yield_from_func(self, code):
+        code.globalstate.use_utility_code(UtilityCode.load_cached("GeneratorYieldFrom", "Coroutine.c"))
+        return "__Pyx_Generator_Yield_From"
+
+
+class AwaitExprNode(_YieldDelegationExprNode):
     # 'await' expression node
     #
     # arg         ExprNode   the Awaitable value to await
     # label_num   integer    yield label number
 
-    is_yield_from = False
     is_await = True
     expr_keyword = 'await'