Python - difference between two strings

Question

I'd like to store a lot of words in a list. Many of these words are very similar. For example I have word afrykanerskojęzyczny and many of words like afrykanerskojęzycznym, afrykanerskojęzyczni, nieafrykanerskojęzyczni. What is the effective (fast and giving small diff size) solution to find difference between two strings and restore second string from the first one and diff?

Answer 1

You can use ndiff in the difflib module to do this. It has all the information necessary to convert one string into another string.

A simple example:

import difflib

cases=[('afrykanerskojęzyczny', 'afrykanerskojęzycznym'),
       ('afrykanerskojęzyczni', 'nieafrykanerskojęzyczni'),
       ('afrykanerskojęzycznym', 'afrykanerskojęzyczny'),
       ('nieafrykanerskojęzyczni', 'afrykanerskojęzyczni'),
       ('nieafrynerskojęzyczni', 'afrykanerskojzyczni'),
       ('abcdefg','xac')] 

for a,b in cases:     
    print('{} => {}'.format(a,b))  
    for i,s in enumerate(difflib.ndiff(a, b)):
        if s[0]==' ': continue
        elif s[0]=='-':
            print(u'Delete "{}" from position {}'.format(s[-1],i))
        elif s[0]=='+':
            print(u'Add "{}" to position {}'.format(s[-1],i))    
    print()      

prints:

afrykanerskojęzyczny => afrykanerskojęzycznym
Add "m" to position 20

afrykanerskojęzyczni => nieafrykanerskojęzyczni
Add "n" to position 0
Add "i" to position 1
Add "e" to position 2

afrykanerskojęzycznym => afrykanerskojęzyczny
Delete "m" from position 20

nieafrykanerskojęzyczni => afrykanerskojęzyczni
Delete "n" from position 0
Delete "i" from position 1
Delete "e" from position 2

nieafrynerskojęzyczni => afrykanerskojzyczni
Delete "n" from position 0
Delete "i" from position 1
Delete "e" from position 2
Add "k" to position 7
Add "a" to position 8
Delete "ę" from position 16

abcdefg => xac
Add "x" to position 0
Delete "b" from position 2
Delete "d" from position 4
Delete "e" from position 5
Delete "f" from position 6
Delete "g" from position 7