compare two lists in python and print the difference

Question

I have two lists and I want to print the difference between them (if there is 1 difference, it should print "1". How can I fix that?

So what I have is:

a= ["1","2","3"]
b= ["1","4","5"]

The answer should be 2.

What do you want for a=["x","y"] and b=["y","x"]? – Stefan Pochmann Feb 18 '16 at 22:57 — Stefan Pochmann, Feb 18 '16 at 22:57

score 3 · Accepted Answer · answered Feb 18 '16 at 22:28

3

It depends on what do you mean by difference. If they are equal in length and you want to find out the difference, do:

c = [i for i in a if i not in b]
print len(c)

answered Feb 18 '16 at 22:28

Shang Wang

I meant the difference like this: A= ["Hai", "Bye", "Python"] B= [ "Hai", "Different11", "different"] --> it should return "2" (because: the lists differs on 2 values) – Feb 18 '16 at 22:37
Have you tried my code? Does it work for you? – Shang Wang Feb 18 '16 at 22:38
Yes I tried, but it didn't work (the result was 0, but should be 1) – Feb 18 '16 at 22:43
What example did you use? – Shang Wang Feb 18 '16 at 22:46
Sorry my mistake. It works! – Feb 18 '16 at 22:54

Kenly · Answer 2 · 2016-02-18T23:00:50.243

1

Use set:

print len(set(L1) - set(L2))

Test:

>>> L1 = [1,2,5]
>>> L2 = [8,1]
>>> len(set(L1) - set(L2))
2

edited Feb 18 '16 at 23:00

answered Feb 18 '16 at 22:28

Kenly

I meant the difference like this: A= ["Hai", "Bye", "Woly"] B= [ "Hai", "Bye", "different"] --> it should return "1" – Feb 18 '16 at 22:33
use WoLy's solution, just print len(r). Or if you need symmetric difference you can use r = list(set(L1) ^ set(L2)) – Joseph James Feb 18 '16 at 22:50
@Loesje Check my edit.It is faster. – Kenly Feb 18 '16 at 23:01

2 Answers2