How to XOR two lists in Python? [duplicate]

Question

I've got two lists, for example:

a = ['hello','world']
b = ['hello','world','im','steve']

If I want to create a third list that only contains elements NOT in both:

c = ['im','steve']

How do I do this if the order of the elements IS important? I know I can use sets but they keep throwing out the order of my lists. I could use ' '.join(list) to convert them to strings but not sure how to do this operation in that format either.

Answer 1

Option 1: set method (recommended)

Sets have a symmetric_difference method that exclusively return elements from either a or b. Order can be preserved with a list comprehension for a concatenated list a + b.

comp = set(a).symmetric_difference(b)
[x for x in a + b if x in comp]
# ['im', 'steve']

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Option 2: pathlib method

For reference, another way to diff two lists might be with pathlib.Path.relative_to method:

import pathlib


p = pathlib.Path(*b)
r = p.relative_to(*a)
list(r.parts)
# ['im', 'steve']

Note: b is the longer list. This option is potentially less efficient than a simple list comprehension.