cached_property reacts gracefully to hasattr (#100)

* add helper to repeatedly await a coroutine

* black formatting

* CacheProperty may be awaited 0 or more times

Author: maxfischer2781

asyncstdlib/functools.py

@@ -6,6 +6,7 @@
     Generic,
     Generator,
     Optional,
+    Coroutine,
     overload,
 )
 
@@ -57,6 +58,25 @@ def __repr__(self) -> str:
         return f"{self.__class__.__name__}({self.value!r})"
 
 
+class _RepeatableCoroutine(Generic[T]):
+    """Helper to ``await`` a coroutine also more or less than just once"""
+
+    __slots__ = ("call", "args", "kwargs")
+
+    def __init__(
+        self, __call: Callable[..., Coroutine[Any, Any, T]], *args: Any, **kwargs: Any
+    ):
+        self.call = __call
+        self.args = args
+        self.kwargs = kwargs
+
+    def __await__(self) -> Generator[Any, Any, T]:
+        return self.call(*self.args, **self.kwargs).__await__()
+
+    def __repr__(self) -> str:
+        return f"<{self.__class__.__name__} object {self.call.__name__} at {id(self)}>"
+
+
 @public_module(__name__, "cached_property")
 class CachedProperty(Generic[T]):
     """
@@ -129,7 +149,7 @@ def __get__(
     ) -> Union["CachedProperty[T]", Awaitable[T]]:
         if instance is None:
             return self
-        return self._get_attribute(instance)
+        return _RepeatableCoroutine(self._get_attribute, instance)
 
     async def _get_attribute(self, instance: object) -> T:
         value = await self.__wrapped__(instance)

asyncstdlib/heapq.py

@@ -111,7 +111,7 @@ def merge(
 def merge(
     *iterables: AnyIterable[T],
     key: Callable[[T], Awaitable[LT]] = ...,
-    reverse: bool = ...
+    reverse: bool = ...,
 ) -> AsyncIterator[T]:
     pass
 
@@ -126,7 +126,7 @@ def merge(
 async def merge(
     *iterables: AnyIterable[Any],
     key: Optional[Callable[[Any], Any]] = None,
-    reverse: bool = False
+    reverse: bool = False,
 ) -> AsyncIterator[Any]:
     """
     Merge all pre-sorted (async) ``iterables`` into a single sorted iterator

unittests/test_itertools.py

@@ -316,7 +316,6 @@ async def values(gby):
 @pytest.mark.parametrize("view", [keys, values])
 @sync
 async def test_groupby(iterable, key, view):
-
     for akey in (key, awaitify(key)):
         assert await view(a.groupby(iterable)) == await view(
             itertools.groupby(iterable)