py/compile: Don't await __aiter__ special method in async-for.

jonathanhogg · dpgeorge · commit 37e1b5c891f9 · 2020-07-25T00:58:18.000+10:00
MicroPython's original implementation of __aiter__ was correct for an earlier (provisional) version of PEP492 (CPython 3.5), where __aiter__ was an async-def function. But that changed in the final version of PEP492 (in CPython 3.5.2) where the function was changed to a normal one. See https://www.python.org/dev/peps/pep-0492/#why-aiter-does-not-return-an-awaitable See also the note at the end of this subsection in the docs: https://docs.python.org/3.5/reference/datamodel.html#asynchronous-iterators And for completeness the BPO: https://bugs.python.org/issue27243 To be consistent with the Python spec as it stands today (and now that PEP492 is final) this commit changes MicroPython's behaviour to match CPython: __aiter__ should return an async-iterable object, but is not itself awaitable. The relevant tests are updated to match. See micropython#6267.
diff --git a/py/compile.c b/py/compile.c
@@ -1798,7 +1798,8 @@ STATIC void compile_async_for_stmt(compiler_t *comp, mp_parse_node_struct_t *pns
     uint try_finally_label = comp_next_label(comp);
 
     compile_node(comp, pns->nodes[1]); // iterator
-    compile_await_object_method(comp, MP_QSTR___aiter__);
+    EMIT_ARG(load_method, MP_QSTR___aiter__, false);
+    EMIT_ARG(call_method, 0, 0, 0);
     compile_store_id(comp, context);
 
     START_BREAK_CONTINUE_BLOCK
diff --git a/tests/basics/async_for.py b/tests/basics/async_for.py
@@ -6,7 +6,7 @@ def __init__(self, obj):
         print('init')
         self._it = iter(obj)
 
-    async def __aiter__(self):
+    def __aiter__(self):
         print('aiter')
         return self
 
diff --git a/tests/basics/async_for2.py b/tests/basics/async_for2.py
@@ -1,4 +1,4 @@
-# test waiting within "async for" aiter/anext functions
+# test waiting within "async for" __anext__ function
 
 import sys
 if sys.implementation.name == 'micropython':
@@ -21,9 +21,8 @@ def __init__(self, high):
         self.cur = 0
         self.high = high
 
-    async def __aiter__(self):
+    def __aiter__(self):
         print('aiter')
-        print('f returned:', await f(10))
         return self
 
     async def __anext__(self):
diff --git a/tests/basics/async_for2.py.exp b/tests/basics/async_for2.py.exp
@@ -1,9 +1,5 @@
 init
 aiter
-f start: 10
-coro yielded: 11
-coro yielded: 12
-f returned: 13
 anext
 f start: 20
 coro yielded: 21
