How to iterate through two lists without the use of nested "for" loops

Question

How do I iterate through two lists without the use of nested "for" loops?

the index between the two lists doesn't necessarily have to be the same

more specifically I am coding a function that takes a list of strings and a list of banned words. If any of the banned words are in each one of the strings, that whole string gets deleted.

I tried doing:

for word in bannedWords:
    for string in messages:
        if word in string:
            messages.remove( string )

This, however, doesn't work because the string variable is used in the "for" loop, so removing the string from messages will mess up the "for" loop. What is a better way to implement? Thanks.

It seems to me you need the nested 'for' loop to do what you want. Your issue is actually: "How do I delete an item from a list while iterating over it?". You can find some answers here: http://stackoverflow.com/questions/1207406/remove-items-from-a-list-while-iterating-in-python — Mel, May 25 '16 at 18:08

UltraInstinct · Accepted Answer · 2016-05-25T18:07:35.453

2

You could probably do it in a line!

messages = [string for string in messages 
              if not any(word in bannedWords for word in string)]

edited May 25 '16 at 18:07

answered May 25 '16 at 18:04

UltraInstinct

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`x` here will be a single letter. – interjay May 25 '16 at 18:05
It would be a word. Let me fix the poor variable naming choice. – UltraInstinct May 25 '16 at 18:07
However you name it, iterating over a string gives individual characters. – interjay May 25 '16 at 18:12
According to OP's code, it seems "messages" are a list of sentences, "string" is a list of words. Iterating over list of strings would give a "word" in each iteration. – UltraInstinct May 25 '16 at 18:15
Thanks for the quick responses guys. Thrustmaster's algorithm seems to work perfectly and was exactly what I was looking for. Been struggling with this for a while. Thanks a lot. – bariox May 25 '16 at 18:15
@Downvoter: Can you please explain? Please consider putting a comment while you downvote.. – UltraInstinct May 25 '16 at 18:18

score 1 · Answer 2 · answered May 25 '16 at 18:03

I would probably write something like:

def filter_messages(messages, bannedWords):
    for string in messages:
        if all(word not in string for word in bannedWords):
            yield string

Now you have a generator function that will only give you good messages. If you really want to update messages in place, you can do:

messages[:] = filter_messages(messages, bannedWords)

though the in-place requirement is rare:

messages = list(filter_messages(messages, bannedWords))

jDo · Answer 3 · 2016-05-25T19:04:05.110

0

Assuming a set of banned words and a list of strings that might contain these bad words:

bannedWords = set("bad", "offensive")

messages = ["message containing a bad word", "i'm clean", "i'm offensive"]

cleaned = [x for x in messages if not any(y for y in bannedWords if y in x)]

Result:

>>> cleaned
["i'm clean"]
>>>

edited May 25 '16 at 19:04

answered May 25 '16 at 18:50

jDo

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How to iterate through two lists without the use of nested "for" loops

3 Answers3