From 8e5b0fdce337ef0a1f4f38b31a8c6b66c56b16d2 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Fri, 23 Oct 2020 18:37:27 -0700 Subject: bpo-19072: Update descriptor howto for decorator chaining (GH-22934) --- Doc/howto/descriptor.rst | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/Doc/howto/descriptor.rst b/Doc/howto/descriptor.rst index 4a53b9e..4e9fad3 100644 --- a/Doc/howto/descriptor.rst +++ b/Doc/howto/descriptor.rst @@ -872,6 +872,16 @@ Using the non-data descriptor protocol, a pure Python version of def __get__(self, obj, cls=None): if cls is None: cls = type(obj) - def newfunc(*args): - return self.f(cls, *args) - return newfunc + if hasattr(obj, '__get__'): + return self.f.__get__(cls) + return types.MethodType(self.f, cls) + +The code path for ``hasattr(obj, '__get__')`` was added in Python 3.9 and +makes it possible for :func:`classmethod` to support chained decorators. +For example, a classmethod and property could be chained together:: + + class G: + @classmethod + @property + def __doc__(cls): + return f'A doc for {cls.__name__!r}' -- cgit v0.12