Is there a cleaner way to write this:
for w in [w for w in words if w != '']:
I want to loop over a dictionary words, but only words that != ''. Thanks!
views:
148answers:
6
+6
A:
You don't need a listcomp here. Just write:
for w in words:
if w != '':
# ...
dan04
2010-05-04 03:27:23
Alright. Worth a shot.
Jasie
2010-05-04 03:31:27
Except List comprehension is the pythonic way of iterating....
Daniel Goldberg
2010-05-04 03:33:21
@Daniel Goldberg, who said that, i thought 'for' was for iterating, and as OP is doing it it is overkill, @dan04 +1, that is the correct way...IMO
Anurag Uniyal
2010-05-04 03:37:01
If you don't want to have another indentation level, you could always have `if w == "": continue` or `if not w: continue`, which is something I see pretty often.
Mike Graham
2010-05-04 03:48:25
@Goldberg: Listcomps are preferred over loops that do .append to a list, not over loops in general.
dan04
2010-05-04 03:49:16
+2
A:
Assuming that you are after the keys, why not try:
[w for w in words if w]
inspectorG4dget
2010-05-04 03:31:45
+1
A:
filter(lambda w: w != '', words) or filter(None, words)
this is suggestion, it may not be the best solution for your problem.
aaa
2010-05-04 03:33:28
"filter(P, S) is almost always written clearer as [x for x in S if P(x)]" - Guido van Rossum.
Noufal Ibrahim
2010-05-04 03:39:01
@Nou I am partial towards functional stuff. at the same time guido really dislike them. they have their place, but probably not for OP problem
aaa
2010-05-04 03:41:09
Your first snippet is a SyntaxError (I think you mean `!=`—`not` is something different). Using `filter` isn't somehow *more functional* than using a list comprehension (an idea we stole from no other but Haskell!), and using `filter` and `map` with lambdas seems downright silly to me.
Mike Graham
2010-05-04 03:46:04
What do you mean by "functional stuff"? Do you mean the name `filter`? How is it semantically different from a list comprehension (which itself was borrowed from a pure functional language)?
Noufal Ibrahim
2010-05-04 04:05:38
@Nou python manual calls them functional tools, hence functional stuff. sometimes I use them because they make code little bit cleaner in certain cases. semantically, that probably not different.
aaa
2010-05-04 04:12:02
Why is this getting voted down? It may not suite some people's taste, but it's entirely valid.
allyourcode
2010-05-04 08:32:41
+1
A:
Testing that an element does not equal '' isn't going to filter out whitespace elements. If that's what you're after, you probably want to use str.isspace (or a regular expression).
If you use a list comprehension, you'll make an extra copy of the list as an intermediary object. Probably not a big deal, but a generator won't use the extra memory.
I'd do it like this, with a generator:
for word in (w for w in words if not w.isspace()):
# do stuff
Matt Anderson
2010-05-04 03:38:11
A:
What does the body of the outer for loop do?
If it's a function call you could potentially just do:
[f(w) for w in words if w != '']
Peter McGrattan
2010-05-04 03:40:14
+1
A:
I think your solution is sub optimal. You're iterating over the list words twice - once in the list comprehension to create the non-null terms and again in the loop to do the processing. It would be better if you used a genexp like so.
for w in (x for x in words if x): process(w)
That way, the genexp will lazily return a list of non-nulls.
Noufal Ibrahim
2010-05-04 03:42:24
`for w in words: if x: process(w)` seems simpler, shorter, and clearer to me.
Mike Graham
2010-05-04 03:49:22