[Python-ideas] Generator syntax hooks?

[Chris Barker]

[...]
> result = []
> for x in sequence:
>     if condition:
>         result.append(expression)
>     else:
>         break
>
> which could be written
>
> [expression for x in sequence if condition break]
>
> It's what I thought too. Adding a `while` clause here just overly
> complicates the understanding of the comprehension. The `break` keyword is
> already easily understandable and helps to map the comprehension with the
> plain for-loop (I like this mapping for its reverse counterpart, as I often
> start with plain for-loops to rewrite them later to comprehensions when it
> makes sense).
>

having the "if condition" there seems confusing to me, particularly if you
want an if condition as a filter as well:

[expression for x in sequence if condition1 if condition2 break]

which makes me want:

[expression for x in sequence if condition1 breakif condition2]

adding another keyword is a pretty big deal though!

would it be possible to add a keyword ("breakif" in this case) that was
ONLY legal in comprehensions?

Though I still dop'nt think using "while" would really introduce that much
confusion -- sure, it doesn't introduce a new loop, but, as someone pointed
out earlier in this thread it really is only changing from a:

"while do"

to a

"do while"

construct -- so means pretty much the same thing.

I agree that scanning a code base to see if there really are many loops in
practice that could use this construct would be a good way to see if there
is any point.

And it would also be interesting to do a survey of "random" folks as to how
they would interpret such a construct -- it's pretty hard for a small group
to know what is and isn't "confusing"

-CHB


-- 

Christopher Barker, Ph.D.
Oceanographer

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Chris.Barker at noaa.gov
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