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 afrykanerskoj?zyczny and many of words like afrykanerskoj?zycznym, afrykanerskoj?zyczni, nieafrykanerskoj?zyczni. 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=[('afrykanerskoj?zyczny', 'afrykanerskoj?zycznym'),
       ('afrykanerskoj?zyczni', 'nieafrykanerskoj?zyczni'),
       ('afrykanerskoj?zycznym', 'afrykanerskoj?zyczny'),
       ('nieafrykanerskoj?zyczni', 'afrykanerskoj?zyczni'),
       ('nieafrynerskoj?zyczni', '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:

afrykanerskoj?zyczny => afrykanerskoj?zycznym
Add "m" to position 20

afrykanerskoj?zyczni => nieafrykanerskoj?zyczni
Add "n" to position 0
Add "i" to position 1
Add "e" to position 2

afrykanerskoj?zycznym => afrykanerskoj?zyczny
Delete "m" from position 20

nieafrykanerskoj?zyczni => afrykanerskoj?zyczni
Delete "n" from position 0
Delete "i" from position 1
Delete "e" from position 2

nieafrynerskoj?zyczni => 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 "?" 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