If i have two lists:
a = [1,2,1,2,4] and b = [1,2,4]
how do i get
a - b = [1,2,4]
such that one element from b removes only one element from a if that element is present in a.
You can use itertools.zip_longest to zip the lists with different length then use a list comprehension :
>>> from itertools import zip_longest >>> [i for i,j in izip_longest(a,b) if i!=j] [1, 2, 4]
>>> list(izip_longest(a,b)) [(1, 1), (2, 2), (1, 4), (2, None), (4, None)]