Python - Compare 2 files and output differences

问题:

I'm aiming to write a script that will compare each line within a file, and based upon this comparison, create a new file containing the lines of text which aren't in the second file.

For example;

**File 1:** 

Bob:20 
Dan:50 
Brad:34 
Emma:32 
Anne:43

**File 2:**

Dan:50
Emma:32
Anne:43

The new output (File 3):

Bob:20
Brad:34

I have some idea of how this needs to be done, but not exactly:

def compare(File1,File2):
   with open(File1, "a") as f1:
       lines = f1.readlines()
       string = line.split(':')
   with open(File2, "a") as f2:
       lines = f2.readlines()
       string2 = line.split(':')
       if string[0] == string[1]:
           with open("newfile2.txt", "w") as f3:
            ....

I think I need something along the lines of this and then to compare the string[0] from each line of each file but I'm really clueless from this point.

Any help would be extremely welcomed.

回答1:

This is working for me:

def compare(File1,File2):
    with open(File1,'r') as f:
        d=set(f.readlines())


    with open(File2,'r') as f:
        e=set(f.readlines())

    open('file3.txt','w').close() #Create the file

    with open('file3.txt','a') as f:
        for line in list(d-e):
           f.write(line)

You need to compare the readlines set and find out lines that are not present in file2. You can then append these lines to the new file.