题目描述：
# Your goal in this kata is to implement a difference function, which subtracts one list from another and returns the result.
#
# It should remove all values from list a, which are present in list b.
#
# array_diff([1,2],[1]) == [2]
# If a value is present in b, all of its occurrences must be removed from the other:
#
# array_diff([1,2,2,2,3],[2]) == [1,3]
我的解答：
def array_diff(a, b):
for i in range(len(a)):
for j in a:
if j in b:
a.remove(j)
return a
网友更加好的方法：
def array_diff(a, b):
return [x for x in a if x not in set(b)]
