Half-baked idea: list comprehensions with "while"

[Roy Smith]

I'm not seriously suggesting this as a language addition, just an interesting idea to simplify some code I'm writing now:

x = [a for a in iterable while a]

which equates to:

x = []
for a in iterable:
if not a:
break
x.append(a)

It does has a few things going for it. It doesn't add any new keywords, nor does it change the meaning of any currently valid program. Whether it's sufficiently useful in general is another question :-) In the specific case I'm looking at now, I've got this annoying lump of code:

valid_answers = []
for p in pairs:
if not all(p):
break
valid_answers.append(p)

which could be rewritten as:

valid_answers = [p for p in pairs while all(p)]

pairs is a list of tuples. I need the leading portion of the list where all elements of the tuple are string non-zero-length strings. Obviously, you'd do the corresponding generator expression as well.

[Kiuhnm]

I think it's a nice idea. In the meantime, try this way:
valid_answers = list(takewhile(all, pairs))

Kiuhnm

[Paul Rubin]

Roy Smith <r...@panix.com> writes:
> x = [a for a in iterable while a]

from itertools import takewhile

x = takewhile(bool, a)

[Kiuhnm]

I see that as a 'temporary' solution, otherwise we wouldn't need 'if'
inside of list comprehensions either.

Kiuhnm

[Miles Rout]

We have if inside list comprehensions? I didn't know that, could you
provide an example?

[Kiuhnm]

elems = [4, 1, 9, 6, 3, 8, 3, 9, 2]
small_elems = [x for x in elems if x < 5]
print str(small_elems) # 4, 1, 3, 3, 2

#leading_small_elems = [x for x in elems while x < 5]
#print str(leading_small_elems) # 4, 1

Kiuhnm