问题
If I have lists:
a = [1, 2, 3, 4, 5]
b = [4, 5, 6, 7, 8]
c = a * b
should give me:
c = [4, 5]
and
c = a - b
should give me:
c = [1, 2, 3]
Is this available for Python or do I have to write it myself?
Would the same work for tuples? I will likely use lists as I will be adding them, but just wondering.
回答1:
If the order doesn't matter, you can use set for this. It has intersection and difference implemented.
>>> a = set([1, 2, 3, 4, 5])
>>> b = set([4, 5, 6, 7, 8])
>>> a.intersection(b)
set([4, 5])
>>> a.difference(b)
set([1, 2, 3])
Here is the info of time complexities of these operations: https://wiki.python.org/moin/TimeComplexity#set. Notice, that the order of subtrahends changes operation complexity.
If element can occur several times (formally it is called multiset), you can use Counter:
>>> from collections import Counter
>>> a = Counter([1, 2, 3, 4, 4, 5, 5])
>>> b = Counter([4, 4, 5, 6, 7, 8])
>>> a - b
Counter({1: 1, 2: 1, 3: 1, 5: 1})
>>> a & b
Counter({4: 2, 5: 1})
来源：https://stackoverflow.com/questions/20179519/is-there-a-way-to-get-the-difference-and-intersection-of-tuples-or-lists-in-pyth