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The docstring of built-in function 'isinstance' should explain that if the classinfo is a tuple, the object must be instance of *any* (not *all*) of the class objects.

It already does:
"The form using a tuple, isinstance(x, (A, B, ...)), is a shortcut
for isinstance(x, A) or isinstance(x, B) or ... (etc.)."
If it were "all", it would use "and", not "or".
I don't think any change is needed. Do you have a suggestion for new wording? If not, I'm going to close this issue.

I agree that the tuple explanation if ok. But "Return whether an object is an instance of a class or of a subclass thereof." (3.5) seems wrong. I believe 'subclass' should be 'superclass'.
 
>>> class C: pass
>>> class Csub(C): pass
>>> isinstance(C(), Csub)
False
>>> isinstance(Csub(), C)
True

On Fri, Jun 26, 2015 at 09:20:18PM +0000, Terry J. Reedy wrote:
> I agree that the tuple explanation if ok. But "Return whether an 
> object is an instance of a class or of a subclass thereof." (3.5) 
> seems wrong. I believe 'subclass' should be 'superclass'.
No, the current description is correct.
> >>> class C: pass
> >>> class Csub(C): pass
> >>> isinstance(C(), Csub)
> False
In this case, the instance C() is an instance of a *superclass* of 
Csub, and isinstance returns False.
> >>> isinstance(Csub(), C)
> True
In this case, the instance Csub() is an instance of a *subclass* of C, 
and isinstance returns True.

Right. Close this unless something else is offered.

Closing. If anyone thinks the docs aren't clear enough, and has an alternate version they would like to suggest, you can re-open it.