On Fri, Aug 30, 2013 at 8:17 AM, Ben Finney <ben+pyt...@benfinney.id.au> wrote:
> Fábio Santos <fabiosantos...@gmail.com> writes:
>
>> It is a shame that this is not possible in python. for..if exists in
>> comprehensions and not in regular loops but that would be nice
>> sometimes.
>
> So you use it in a generator expression, and iterate over the generator:
>
> for foo in (spam for spam in sequence if predicate(spam)):
> process(spam)
>
> That way, there's no need for new syntax.
That works for the specific example of a for loop (and proves that
it's logical and sensible to iterate over part of a loop). But how
many times has something similar come up - like the
while-loop-that-retains-its-value suggestion a while ago? Sometimes,
the only "new syntax" required is a weakening of the rule that one
thing goes on one line, and then the syntax is simply two block
constructs forming a single loop header.
Also, the genexp version you have above seems to repeat itself a lot.
I'd write that as simply:
for spam in sequence: if predicate(spam):
process(spam)
though of course, if the processing is a single function call, there
are other ways to lay it out. But assume that the processing is a full
suite.
ChrisA
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