compare two lists (python)

Question

I need to compare two lists in a program to see if there are matching strings. One of them is a txt document that I already imported. Thats what I did

    def compareLists(self, listA, listB):
    sameWords = list()

    for a in xrange(0,len(listA)):
        for b in xrange(0,len(listB)):
            if listA[a] == listB[b]:
                sameWords.append(listA[a])
                pass
            pass
        pass
    return sameWords

But if I run the program it doesnt show any matches although I know that there has to be one. I think its somewhere inside the if block.

have you tried out a debugger? You can easily observe, which values listA or listB have in each iteration step. — Rockbar, Oct 09 '16 at 17:38
`list(set(listA) & set(listB))` will return exactly what you want, as shown [here](http://stackoverflow.com/questions/642763/python-intersection-of-two-lists). — Efferalgan, Oct 09 '16 at 17:39
I'm surprised actually that this doesn't show matches. Even though it is inefficient and the `pass` is unnecessary, it should still give you a list of all the matches found (with duplicates included). — Jack Ryan, Oct 09 '16 at 17:43
it's working fine for input : `listA=['hiii','kkkk'] listB=['jiii','ggg','hiii']` it gives : `['hiii']` as output. I tried in Python online compiler. — Kalpesh Dusane, Oct 09 '16 at 17:44
It's working too if I dont use a list that imported a .txt file but with the .txt its not working. — Lucas Mähn, Oct 09 '16 at 17:48
Do a `print()` of the list made from the imported file. My guess is that the words it contains are ending with `\n`. — Efferalgan, Oct 09 '16 at 17:50

Jack Ryan · Accepted Answer · 2016-10-09T18:05:39.547

1

I am assuming the indentation is correct in your code. Continuing with your strategy, this code should work.

def compareLists(self, listA, listB):
    sameWords = list()

    for a in xrange(0,len(listA)):
        for b in xrange(0,len(listB)):
            if listA[a] == listB[b]:
                sameWords.append(listA[a])
    return sameWords

Alternatively, as @Efferalgan suggested, simply do the set intersection.

def compareLists(self, listA, listB):
    return list(set(listA) & set(listB))

Note: The set intersection will remove duplicate matching words from your result.

As you said, you are reading in the lines from a text file, and it looks like the newlines are still in there.

my_text_list = [s for s in open("my_text.txt").read().rsplit()]

edited Oct 09 '16 at 18:05

answered Oct 09 '16 at 17:45

Jack Ryan

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It's still not working. Im pretty sure its because of the .txt file but i can print it out as a list so I imported it right. Could it be possible that the file is just too big? It has about 15,000 lines – Lucas Mähn Oct 09 '16 at 17:52
The size of the list should not matter, it is not *that* big. Print the list, and visually check that the words in it are what you expect. – Efferalgan Oct 09 '16 at 17:55
15,000 lines should be fine. Could you post some of the list that you printed? – Jack Ryan Oct 09 '16 at 17:55
'Weiltingen\n', 'Unterschwaningen\n', 'Theilenhofen\n', 'R\xc3\xb6ckingen\n', 'Pfofeld\n', 'Ornbau\n', 'Muhr am See\n', – Lucas Mähn Oct 09 '16 at 17:59
After I removed the \n s its showing this: > (Its scrapy btw) – Lucas Mähn Oct 09 '16 at 18:00
Call `.rsplit()` on the strings to remove the newlines when you read in the file. – Jack Ryan Oct 09 '16 at 18:02
Okay I got it. thank you very much guys and sorry if this question might be a little bit stupid, Im a little bit new to that. – Lucas Mähn Oct 09 '16 at 18:13

compare two lists (python)

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