Python reading lines in nested for loops from two files

问题

I want to match the lines of one text file with another text file, line by line, there is a problem with my nested for loops, it must be simple, but I can't find it,

for line1 in ratings:
    cont1+=1

    for line2 in movies:
         cont2+=1
         print(cont1,cont2)

I simplified it with this loops, to check the error, The outer loop doesn't reach cont=2,

1 1
1 2
1 3
1 4
1 5
1 6
1 7
.
.
.
1 157
>>>

回答1:

you need to loop over both files simultaneously

ratings= open('ratings.txt')
movies= open('movies.txt')

for rating, movie in itertools.izip(ratings, movies):
    # do task

or

ratings= open('ratings.txt').readlines()
movies= open('movies.txt').readlines()

for rating, movie in zip(ratings, movies):
    # do task

回答2:

The problem is that I need to reset the inner loop with seek(0), doing that the loop works properly, thanks to everyone for your replies.

回答3:

Your implementation runs for every line in file1 run all line in file2,

the actual code shd be,

for line1,line2 in zip(ratings,movies):
 cont1+=1
 cont2+=1
 print(cont1,cont2)

回答4:

with open('ratings.txt') as ratings, open('movies.txt') as movies:
    for rating, movie in itertools.izip(ratings, movies):
        # do task

This is an improvement on avasal's answer in that it picks up the lines iteratively (equivalent to the old xreadlines that is now deprecated) rather than reading all the lines in via readlines(). So it should read a line from each, then process them, then read another line etc, permitting Files Of Enormity where readlines implementation would be limited to smaller files.

Note that izip continues until one of the iterators stops, so you'll only get as many rows as the shorter file. I'm assuming that's correct, however, since the code implicitly assumes the two files match anyway.

来源：https://stackoverflow.com/questions/13137969/python-reading-lines-in-nested-for-loops-from-two-files