'while' in list comprehension?

[Michael Geary]

> > > wouldn't it be useful to have a 'while' conditional in addition to
> > > 'if' in list comprehensions?
> > >
> > >     foo = []
> > >     for i in bar:
> > >         if len(i) == 0:
> > >             break
> > >         foo.append(i)
> > >
> > > would then turn into
> > >
> > >     foo = [ i for i in bar while len(i)>0 ]
> >
> > while is simply not same as if: break!
> > if executes once for each value of i, while indefinitely.
> > If you translate back by current rule, which will not change, you get:
> >
> > foo = []
> > for i in bar:
> >     while len(i) >0:
> >          foo.append(i)
>
> I agree that 'while' cannot not just be considered a replacement
> for 'if'. However, adding a 'while' conditional to list
> comprehensions would very unlikely be misunderstood as another
> (infinite) loop. Instead, I find the above 'while' example about
> as intuitive as is the case with 'if'. It simply means that under
> a certain condition the loop will be ended, which is just what
> most people would probably expect.

Here's an idea that might avoid this bit of confusion:

    foo = [ i for i in bar until len(i) == 0 ]

That also makes the conditional test the same as used in the "if/break"
form.

Hmm... Would this mean that "until" would have to become a reserved word?
Maybe not such a good idea if that's the case.

-Mike