From 12a2e41e8a276ec3a68f3e5f94b02752185c66fb Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Sat, 19 Feb 2022 23:02:30 -0600 Subject: [PATCH] Improve discussion about how __getattr__ is invoked. (GH-31435) --- Doc/howto/descriptor.rst | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-) diff --git a/Doc/howto/descriptor.rst b/Doc/howto/descriptor.rst index 4f6389e3b2d..825e9d0347f 100644 --- a/Doc/howto/descriptor.rst +++ b/Doc/howto/descriptor.rst @@ -696,10 +696,14 @@ a pure Python equivalent: >>> b.g == b['g'] == ('getattr_hook', b, 'g') True +Note, there is no :meth:`__getattr__` hook in the :meth:`__getattribute__` +code. That is why calling :meth:`__getattribute__` directly or with +``super().__getattribute__`` will bypass :meth:`__getattr__` entirely. -Interestingly, attribute lookup doesn't call :meth:`object.__getattribute__` -directly. Instead, both the dot operator and the :func:`getattr` function -perform attribute lookup by way of a helper function: +Instead, it is the dot operator and the :func:`getattr` function that are +responsible for invoking :meth:`__getattr__` whenever :meth:`__getattribute__` +raises an :exc:`AttributeError`. Their logic is encapsulated in a helper +function: .. testcode:: @@ -744,12 +748,6 @@ perform attribute lookup by way of a helper function: ... AttributeError: 'ClassWithoutGetAttr' object has no attribute 'z' -So if :meth:`__getattr__` exists, it is called whenever :meth:`__getattribute__` -raises :exc:`AttributeError` (either directly or in one of the descriptor calls). - -Also, if a user calls :meth:`object.__getattribute__` directly, the -:meth:`__getattr__` hook is bypassed entirely. - Invocation from a class -----------------------