Subtracting two lists in Python

Question

In Python, How can one subtract two non-unique, unordered lists? Say we have a = [0,1,2,1,0] and b = [0, 1, 1] I\'d like to do something like

Answer 1

I attempted to find a more elegant solution, but the best I could do was basically the same thing that Dyno Fu said:

from copy import copy

def subtract_lists(a, b):
    """
    >>> a = [0, 1, 2, 1, 0]
    >>> b = [0, 1, 1]
    >>> subtract_lists(a, b)
    [2, 0]

    >>> import random
    >>> size = 10000
    >>> a = [random.randrange(100) for _ in range(size)]
    >>> b = [random.randrange(100) for _ in range(size)]
    >>> c = subtract_lists(a, b)
    >>> assert all((x in a) for x in c)
    """
    a = copy(a)
    for x in b:
        if x in a:
            a.remove(x)
    return a