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Code Issues Releases Wiki Activity

Improve discussion about how __getattr__ is invoked. (GH-31435)

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Raymond Hettinger 2022-02-19 23:02:30 -06:00 committed by GitHub
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Doc/howto/descriptor.rst
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@ -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
-----------------------