bpo-46622: Async support for cached_property #31314
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The functools.cached_property can now decorate an async function. It would cache a wrapper to the coroutine returned by the function, and await it when the wrapper is first awaited.
| val = cache.get(self.attrname, _NOT_FOUND) | ||
| if val is _NOT_FOUND: | ||
| val = self.func(instance) | ||
| if inspect.iscoroutinefunction(self.func): |
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inspect.isawaitable(val) check covers more cases, please use it.
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This would change the behaviour of
class MyAwaitable:
def __await__(self):
print("called")
class Foo:
@cached_property
def get_awaitable(self):
return MyAwaitable()Currently this would cache the MyAwaitable object and calls __await__. If we use isawaitable here, MyAwaitable would be wrapped and only awaited once.
IMO iscoroutinefunction is more correct here.
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| def __get__(self, instance, owner=None): | ||
| import inspect |
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Please move the import just before usage, when the attribute name is not in cache yet.
The import instruction is not for free, it requires a lock at least IIRC.
The move allows returning cached results as fast as possible.
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| class _CachedAwaitable: | ||
| """Wrapper to return if @cached_proeprty is used on a coroutine function. |
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spelling: cached_property
| A coroutine shouldn't simply be cached since it can only be awaited once. | ||
| This wrapper is cached instead, which awaits the underlying coroutine at | ||
| most once and cache the result for subsequent calls. |
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Closing for now to work on |
The functools.cached_property can now decorate an async function. It would cache a wrapper to the coroutine returned by the function, and await it when the wrapper is first awaited.
https://bugs.python.org/issue46622