Check if there are new strings in a txt file

Question

I am trying to make a function which will compare two txt files. If it recognizes new lines that are in one file but not in the other, it will add them in a list and also in that file that does not contain those new lines. It fails to do that. Here is my function. What am I doing wrong?

newLinks = []

def newer():
with open('cnbcNewLinks.txt', 'w') as newL:
    for line in open('cnbcCleanedLinks.txt'):
        if line not in "cnbcNewLinks.txt":
            newLinks.append(line)
            newL.write(line)
        else:
            continue
cleaned = ''.join(newLinks)
print(cleaned)

`if line not in "cnbcNewLinks.txt":` is just testing the text string of the filename, it is *not* searching the file. — cdarke, Apr 27 '17 at 07:48
Use the file handle `newL`, as you already do when writing to the file. — Christian König, Apr 27 '17 at 07:54
Not a very efficient way of doing it, but you could just change `if line not in "cnbcNewLinks.txt"` to `if line not in open("cnbcNewLinks.txt").readlines()` and it should probably work. A more pragmatic way would be to have a double loop. — Gustavo Bezerra, Apr 27 '17 at 07:57
Check out this question: http://stackoverflow.com/questions/19120489/compare-two-files-report-difference-in-python — gushitong, Apr 27 '17 at 08:35

score 1 · Answer 1 · answered Apr 27 '17 at 07:59

1

If files not big, then move data in list, both of list convert in set and use 'differ' builtin functions, two times. then add difference in files.

answered Apr 27 '17 at 07:59

Alex

37
4

Kruupös · Accepted Answer · 2017-04-27T14:54:31.570

I put in python code what @Alex suggested.

See the doc for set.

I replace you text file name by a.txt and b.txt to be easily readable.

# First read the files and compare then using `set`
with open('a.txt', 'r') as newL, open('b.txt', 'r') as cleanL:
    a = set(newL)
    b = set(cleanL)
    add_to_cleanL = list(a - b) # list with line in newL that are not in cleanL
    add_to_newL = list(b - a) # list with line in cleanL that are not in newL

# Then open in append mode to add at the end of the file
with open('a.txt', 'a') as newL, open('b.txt', 'a') as cleanL:
    newL.write(''.join(add_to_newL)) # append the list at the end of newL
    cleanL.write(''.join(add_to_cleanL)) # append the list at the end of cleanL

Check if there are new strings in a txt file

2 Answers2