[Python-ideas] Updating PEP 315: do-while loops
rrr at ronadam.com
Tue Apr 28 08:58:50 CEST 2009
Terry Reedy wrote:
> A quick summary of my views:
> 1. When I programmed in C, I hardly if ever used do...while. I have
> read that this is true of other C coders also. So I see no need for a
> Python equivalent.
> 2. On the other hand, loop and a half use is a regular occurrence.
> Anything that does not arguably improve
> while True:
> if cond: break
> such as
> whhile not cond:
> seems pretty useless. But even the above does not work great for
> multiple "if... break"s and not at all for "if...continue".
I agree. I don't see lack of do--while as a wart.
> 3. I do not see 'if cond: break' as that much of a problem. One can
> emphasize with extra whitespace indent or comment.
> if cond: break #EXIT#
> In any case, I see it as analogous to early return
> def f():
> if cond: return
> and while there are purists who object to *that*, I have not seen any
> proposals to officially support better emphasis (other than the existing
> whitespace or comment mechanisms).
> In fact, it is not uncomment to use 'return expr' instead of 'ret=expr;
> break' when a loop (for or while) is the last part of a def.
The 'break if'/'continue if' would make the break and continue more visible
in some cases, but I now realize it also is limited to a single line rather
than a block.
Break and continue are pretty visible as long as they are on a line by
themselves, so maybe we should just stick with what we have.
> 4. "do ... while cond:" strikes me as ugly. Aside from that, I do not
> like and would not use anything that puts the condition out of place,
> other than where it is executed. I would hate to read such code and
> expect it would confuse many others.
> 5. We well never reach consensus. PEP 315 might as well be withdrawn.
Unless there is some very nice examples or performance reasons to show
otherwise, I just don't see enough need to be a convincing change.
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