How can I compare two lists?

Question

I'm asked to compare two different string and return the dis-matches. And if one string is longer than another, come out the extra characters.

characters1=list(contents1)
characters2=list(contents2)
for (a,b) in zip(characters1, characters2):    
    if a != b:
        print('Mismatch at character', characters1.index(a), a, '!=', b)

Here is what I have done and I cannot figure out the extra part.

http://stackoverflow.com/questions/3462143/get-difference-between-two-lists — Maroun, May 26 '15 at 08:19
Not related to the question directly, but `characters1.index(a)` won't return what you expect in case if the mismatching character is seen before in that string. — bereal, May 26 '15 at 08:19

bereal · Answer 1 · 2015-05-26T08:40:04.107

I'd use itertools.izip_longest here, something like:

for idx, (a, b) in enumerate(izip_longest(s1, s2)):
    if a and b:
        if a != b:
            print 'Mismatch at {0}: {1} != {2}'.format(idx, a, b)
    else:
        suffix = (s1 if a else s2)[idx:]
        print 'Extra string: {0}'.format(suffix)
        break

Notice also that index() returns the first entrance of the item, so that might return a wrong result if the character repeats in the string. enumerate is the way to go. Converting strings to lists is also redundant, strings are already iterable.

score 0 · Answer 2 · answered May 26 '15 at 08:21

Compare their length:

if len(a)>len(b):
    print("a is longer than b by %s" % str(len(a)-len(b))) 
    print("Extra part is %s" % a[len(b):])
elif len(a)<len(b):
    print("a is shorter than b by %s" % str(len(b)-len(a)))
    print("Extra part is %s" % b[len(a):])

Vincent · Answer 3 · 2015-05-26T08:49:14.737

0

>>> a = "xyz"
>>> b = "abcdef"
>>> a[len(b):] or b[len(a):]
'def'

Also, as @bereal pointed out, characters1.index(a) won't work as you expect. You could consider using enumerate:

for i, (a, b) in enumerate(zip(characters1, characters2)):    
    if a != b:
        print('Mismatch at character', i, ':', a, '!=', b)
print('Extra string:', characters1[i+1:] or characters2[i+1:])

edited May 26 '15 at 08:49

answered May 26 '15 at 08:22

Vincent

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score 0 · Answer 4 · answered May 26 '15 at 08:23

0

Something like this:

if len(characters1) > len(characters2):
     print('Extra characters1: ', characters1[len(characters2):])
elif len(characters2) > len(characters1):
     print('Extra characters2: ', characters2[len(characters1):])

answered May 26 '15 at 08:23

Eugene Soldatov

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score 0 · Answer 5 · answered May 26 '15 at 08:35

This shows how to compare the two lists, and will properly compare two different strings of equal length:

a = ['abc', 'def', 'ghi']
b = ['abc', 'ddf', 'ghij']

for x,y in zip(a, b):
    if x!=y:
        print(x, y, x[len(y):] if len(x)>len(y) else y[len(x):])

Prints:

def ddf
ghi ghij j

How can I compare two lists?

5 Answers5