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

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 #6267.
This commit is contained in:
Jonathan Hogg 2020-07-21 18:47:28 +01:00 committed by Damien George
parent fe7d47971f
commit 37e1b5c891
4 changed files with 5 additions and 9 deletions

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@ -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

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@ -6,7 +6,7 @@ class AsyncIteratorWrapper:
print('init')
self._it = iter(obj)
async def __aiter__(self):
def __aiter__(self):
print('aiter')
return self

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@ -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 @@ class ARange:
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):

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@ -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