Get difference between two lists

python performance list set set-difference
Max Frai picture Max Frai · Aug 11, 2010 · Viewed 868.3k times · Source

I have two lists in Python, like these:

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

I need to create a third list with items from the first list which aren't present in the second one. From the example I have to get:

temp3 = ['Three', 'Four']

Are there any fast ways without cycles and checking?

Answer

ars picture ars · Aug 11, 2010 
In [5]: list(set(temp1) - set(temp2))
Out[5]: ['Four', 'Three']

Beware that 

In [5]: set([1, 2]) - set([2, 3])
Out[5]: set([1])

where you might expect/want it to equal set([1, 3]). If you do want set([1, 3]) as your answer, you'll need to use set([1, 2]).symmetric_difference(set([2, 3])).

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