Path decorators: allow empty docstrings to support embedded Python

src/trio/_path.py

@@ -38,12 +38,12 @@ async def wrapper(*args: P.args, **kwargs: P.kwargs) -> T:
             return await run_sync(partial(fn, *args, **kwargs))
 
         update_wrapper(wrapper, wrapped)
-        assert wrapped.__doc__ is not None
-        wrapper.__doc__ = (
-            f"Like :meth:`~{wrapped.__module__}.{wrapped.__qualname__}`, but async.\n"
-            f"\n"
-            f"{cleandoc(wrapped.__doc__)}\n"
-        )
+        if wrapped.__doc__:
+            wrapper.__doc__ = (
+                f"Like :meth:`~{wrapped.__module__}.{wrapped.__qualname__}`, but async.\n"
+                f"\n"
+                f"{cleandoc(wrapped.__doc__)}\n"
+            )
         return wrapper
 
     return decorator
@@ -76,23 +76,23 @@ def _wrap_method_path_iterable(
     def wrapper(self: PathT, /, *args: P.args, **kwargs: P.kwargs) -> Iterable[PathT]:
         return map(self.__class__, [*fn(self._wrapped_cls(self), *args, **kwargs)])
 
-    assert wrapper.__doc__ is not None
-    wrapper.__doc__ += (
-        f"\n"
-        f"This is an async method that returns a synchronous iterator, so you\n"
-        f"use it like:\n"
-        f"\n"
-        f".. code:: python\n"
-        f"\n"
-        f"    for subpath in await mypath.{fn.__name__}():\n"
-        f"        ...\n"
-        f"\n"
-        f".. note::\n"
-        f"\n"
-        f"    The iterator is loaded into memory immediately during the initial\n"
-        f"    call (see `issue #501\n"
-        f"    <https://github.com/python-trio/trio/issues/501>`__ for discussion).\n"
-    )
+    if wrapper.__doc__:
+        wrapper.__doc__ += (
+            f"\n"
+            f"This is an async method that returns a synchronous iterator, so you\n"
+            f"use it like:\n"
+            f"\n"
+            f".. code:: python\n"
+            f"\n"
+            f"    for subpath in await mypath.{fn.__name__}():\n"
+            f"        ...\n"
+            f"\n"
+            f".. note::\n"
+            f"\n"
+            f"    The iterator is loaded into memory immediately during the initial\n"
+            f"    call (see `issue #501\n"
+            f"    <https://github.com/python-trio/trio/issues/501>`__ for discussion).\n"
+        )
     return wrapper
 
 

src/trio/_tests/test_path.py

@@ -252,3 +252,21 @@ async def test_classmethods() -> None:
 
     # Wrapped method has docstring
     assert trio.Path.home.__doc__
+
+
+@pytest.mark.parametrize(
+    "wrapper",
+    [
+        trio._path._wraps_async,
+        trio._path._wrap_method,
+        trio._path._wrap_method_path,
+        trio._path._wrap_method_path_iterable,
+    ],
+)
+def test_wrapping_without_docstrings(
+    wrapper: Callable[[Callable[[], None]], Callable[[], None]]
+) -> None:
+    @wrapper
+    def func_without_docstring() -> None: ...
+
+    assert func_without_docstring.__doc__ is None