Get difference between two lists

Question

I have two lists in Python, like these:

temp1 = [\'One\', \'Two\', \'Three\', \'Four\']
temp2 = [\'One\', \'Two\']

I need to create a third

Answer 1

Here's a Counter answer for the simplest case.

This is shorter than the one above that does two-way diffs because it only does exactly what the question asks: generate a list of what's in the first list but not the second.

from collections import Counter

lst1 = ['One', 'Two', 'Three', 'Four']
lst2 = ['One', 'Two']

c1 = Counter(lst1)
c2 = Counter(lst2)
diff = list((c1 - c2).elements())

Alternatively, depending on your readability preferences, it makes for a decent one-liner:

diff = list((Counter(lst1) - Counter(lst2)).elements())

Output:

['Three', 'Four']

Note that you can remove the list(...) call if you are just iterating over it.

Because this solution uses counters, it handles quantities properly vs the many set-based answers. For example on this input:

lst1 = ['One', 'Two', 'Two', 'Two', 'Three', 'Three', 'Four']
lst2 = ['One', 'Two']

The output is:

['Two', 'Two', 'Three', 'Three', 'Four']