[Python-ideas] Allowing breaks in generator expressions by overloading the while keyword

[David Mertz]

This seems *so* close to what itertools.takewhile() does that it's really
hard for me to see why we need special syntax for it.


On Thu, Feb 20, 2014 at 6:13 PM, Carl Smith <carl.input at gmail.com> wrote:

> Sometimes you need to build a list in a loop, but break from the loop if
> some condition is met, keeping the list up to that point. This is so common
> it doesn't really need an example.
>
> Trying to shoehorn the break keyword in to the generator expression syntax
> doesn't look pretty, unless you add `and break if expr` to the end, but
> that has its own issues. Besides, overloading `while` is much cuter...
>
>     ls = [ expr for name in iterable while expr ]
>
>     ls = [ expr for name in iterable if expr while expr ]
>
>     ls = [ expr for name in iterable if expr else expr while expr ]
>
> With regular generator expressions, it gives you a kind of base case,
> which may assist with showing off.
>
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