[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Steven D'Aprano added the comment: The plot thickens. I was wrong to say that type() always and only looks at the "real" underlying type of the instance. type() does look at __class__ as well. But only sometimes. >>> class A: ... __class__ = int ... >>> type(A()) >>> a = A() >>>

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Gabriele N Tornetta added the comment: @rhettinger Apologies. You're totally right but I wasn't expecting this to become a lengthy conversation. So, to get closer to the initial issue, I believe that this ticket could be closed provided that the documentation is improved by making

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Steven D'Aprano added the comment: On Fri, Dec 10, 2021 at 12:03:15AM +, Gabriele N Tornetta wrote: > class Side(object): > def __getattribute__(self, name): > ValueError(name) You forgot to actually *raise* the exception. That will just instantiate the ValueError instance,

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Steven D'Aprano added the comment: I agree that the rules regarding type and `__class__` and isinstance are not clear or well documented. We have: https://docs.python.org/3/library/stdtypes.html#instance.__class__ https://docs.python.org/3/library/functions.html#isinstance but neither

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Raymond Hettinger added the comment: > Changing the way isinstance works internally might prove > beneficial for such tools. ISTM you're advocating a design change rather than discussing a bug report. The python-ideas mail list would be a better forum than the tracker. -- nosy:

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Gabriele N Tornetta added the comment: > Python is very much a language about responsibility. If Django is overriding > `__getattribute__` then it is their responsibility to ensure that everything > still works properly. Perhaps I didn't stress observability enough. A tool like a tracer or

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Ethan Furman added the comment: $ python3 Python 3.8.10 (default, Sep 28 2021, 16:10:42) [GCC 9.3.0] on linux Type "help", "copyright", "credits" or "license" for more information. >>> object >>> import builtins >>> builtins.object >>> builtins.object = int >>> object Python is very

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Gabriele N Tornetta added the comment: > I tend to agree with Steven and David here. You define __getattribute__ and > so that's the behaviour you get when an attribute of the class is requested > (whether by the system or by your code). I would agree if it was obvious or explicitly stated

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Paul Moore added the comment: I tend to agree with Steven and David here. You define __getattribute__ and so that's the behaviour you get when an attribute of the class is requested (whether by the system or by your code). The documentation (here:

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Steven D'Aprano added the comment: If you don't want to customise attribute access, don't overload `__getattribute__`. The documentation for `__getattribute__` is clear about what it does: "Called unconditionally to implement attribute accesses for instances of the class."

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Gabriele N Tornetta added the comment: I think the issue on display here is that isinstance could cause a side effect, which I dare say it's unexpected (and not documented AFAIK). Are there any reasons why __class__ cannot be retrieved with object.__getattribute__ instead? In fact,

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Steven D'Aprano added the comment: I'd be inclined to see this as a bug in your code, if you are causing side-effects from `__getattribute__`. If you don't want attribute access to cause side-effects, then don't put code in `__getattribute__` that causes side-effects :-) isinstance has to

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Gabriele N Tornetta added the comment: The following example shows isinstance causing a side effect class Side: class Effect(Exception): pass def __getattribute__(self, name): raise Side.Effect() isinstance(Side(), str) I'd be inclined to see this as a bug as I

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

Steven D'Aprano added the comment: Dan, I don't understand what you think the code snippet shows: you're calling isclass on an object which *actually is a class* and show that it returns True. What did you expect it to return? How does the code snippet you give

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

R. David Murray added the comment: I don't think this is a bug. There are many ways to lie in Python. If your object lies, it is on your head when things break :) On the flip side, the ability to lie is very handy in many circumstances, and is often a case of duck

[issue32683] isinstance is calling ob.__getattribute__ as a fallback instead of object.__class__.__get__

New submission from Dan Snider : It doesn't even care if the result it gets from ob.__getattribute__("__class__") isn't a type. Surely `isinstance` is intended to do what it is named and be guaranteed to return True if an object `ob` is an instance of class `cls`.