On Wed, Aug 1, 2018 at 5:29 PM, Jonathan Fine <jfine2...@gmail.com> wrote: > Hi All > > I have two further questions. I'm keen to clarify what is the > behaviour specified by PEP 505. I'm not, at this time, interested in > why and how PEP 505 specifies behaviour. I just wish, through explicit > examples, to clarify the behaviour that is specified. > > Here 'a' is an identifier. Consider the following 12 expressions (I > use the word loosely). > > 1) a . b . c > 2) (a . b) . c > 3) a . (b . c) > > 4) a ?. b . c > 5) (a ?. b) . c > 6) a ?. (b . c) > > 7) a . b ?. c > 8) (a . b) ?. c > 9) a . (b ?. c) > > 10) a ?. b ?. c > 11) (a .? b) ?. c > 12) a ?. (b ?. c) > > Question A: Which of the expressions are NOT valid (Python + PEP 505) syntax? > Question B: Which of the valid (Python + PEP 505) expressions are > equivalent, for all possible values of 'a'. > > The answer depends, of course, on the exact text of PEP 505. I've not > read PEP 505 that closely. My expectations, based on my Python > experience, are that PEP 505 would be written so that: > > Answer A: Expressions 3, 6, 9 and 12 are invalid. The others are valid.
Correct. After a dot (whether ?. or plain . ), you need a NAME, not any form of expression (test, expr, etc). > Answer B: 1 and 2 are equivalent. Similarly 4 and 5. Similarly 7 and > 8. Similarly 10 and 11. There are no other equivalences (for all > values of 'a'). Incorrect. The short-circuiting behaviour ends at any sort of grouping. It's like how "a < b < c" is not equivalent to "(a < b) < c", nor to "a < (b < c)". ChrisA _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
