Hi Stephan You wrote
> Let me stand up and claim that if a chain consists *only* of None-coalescing > operations, then breaking up the chain by adding parentheses does not > matter, ever. You missed a post I made, 17 minutes before yours. I then believed that PEP 505 specified. #1. (None ?. dne) is None #2. (None ?. dne ?. __str__) is None #3. (None.__str__) is not None #4. ((None ?. dne) ?. __str__) is (None.__str__) After my last post, you wrote > None.?__str__ > produces None, even though None has a __str__ attribute. This surprises me. But I think it follows from the rules in https://www.python.org/dev/peps/pep-0505/#the-maybe-dot-and-maybe-subscript-operators My initial reading of >>> a ?. b was that if 'a' didn't have a 'b' attribute, then the result was None, whatever the string 'b'. In other words, the same as >> getattr(a, name, None) But you and I agree, I think, that PEP 505 specifies (in the cited page fragment) >>> a ?. anything is always None, whenever 'a' is None, and for any non-keyword identifier instead of 'anything'. Thank you for contributing this clarification. The abstract to PEP 505 writes === The "None-aware attribute access" operator ?. ("maybe dot") evaluates the complete expression if the left hand side evaluates to a value that is not None === This is, of course, informal prose. I'm now reading it carefully. Here's a specific example. >>> (42).__str__ <method-wrapper '__str__' of int object at 0x99f480> >>> (42).str Traceback (most recent call last): AttributeError: 'int' object has no attribute 'str' >>> (42) ?. str I don't see how to apply the prose in the abstract to this last example. The left hand side is not None, so we "evaluate the complete expression". On one reading, this is a recursion. I'd very much appreciate some help here. -- Jonathan _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
