Le 21/04/2020 à 18:32, Dieter Maurer a écrit :
ast wrote at 2020-4-21 14:27 +0200:
I recently read the Python (3.9a5) documentation - and there
I found clearly expressed this behaviour (I no longer can
tell you exactly where I read this).
The reason comes from the implementation: when the descriptor
is instantiated, the name the instance is bound to is not yet known.
Class creation is complex in Python (details in the Python documentation):
first a so called "namespace" (a mapping from names to values) is constructed;
after this construction, the so called metaclass is called with
class name, bases, the constructed namespace and potentially additional
keyword arguments. It is the typical metaclass (`type`) which calls
`__set_name__` for descritors it finds in the namespace.
This has several ramifications:
* `__set_name__` is not called "inline" (as you observed)
* `__set_name__` is not called automatically for descriptors added
after class construction
* `__set_name_` may not be called at all if the class uses
a custom metaclass.
Thank you for this explanation.
So it's not a bug it's a feature
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