MRAB writes: > On 2017-08-10 15:28, Steve D'Aprano wrote:
>> Every few years, the following syntax comes up for discussion, with >> some people saying it isn't obvious what it would do, and others >> disagreeing and saying that it is obvious. So I thought I'd do an >> informal survey. >> >> What would you expect this syntax to return? >> >> [x + 1 for x in (0, 1, 2, 999, 3, 4) while x < 5] >> >> >> For comparison, what would you expect this to return? (Without >> actually trying it, thank you.) >> >> [x + 1 for x in (0, 1, 2, 999, 3, 4) if x < 5] >> >> >> >> How about these? >> >> [x + y for x in (0, 1, 2, 999, 3, 4) while x < 5 for y in (100, 200)] >> >> [x + y for x in (0, 1, 2, 999, 3, 4) if x < 5 for y in (100, 200)] >> >> >> >> Thanks for your comments! >> > There's a subtlety there. > > Initially I would've thought that the 'while' would terminate the > iteration of the preceding 'for', but then when I thought about how I > would expand it into multiple lines, I realised that the 'while' would > have to be expanded to "if x < 5: break", not an inner 'while' loop. I wonder how such expansions would work in general. [x + y for x in (0, 1, 2, 999, 3, 4) for y in (100, 200) while x < 5] [x + y for x in (0, 1, 2, 999, 3, 4) for y in (100, 200) while x < y] -- https://mail.python.org/mailman/listinfo/python-list
