Python set集合方法详解（全）

前面学习了 set 集合，本节来一一学习 set 类型提供的方法。首先，通过 dir(set) 命令可以查看它有哪些方法：

>>> dir(set)
['add', 'clear', 'copy', 'difference', 'difference_update', 'discard', 'intersection', 'intersection_update', 'isdisjoint', 'issubset', 'issuperset', 'pop', 'remove', 'symmetric_difference', 'symmetric_difference_update', 'union', 'update']

各个方法的具体语法结构及功能如表 1 所示。

表 1 Python set方法 方法名 语法格式 功能 实例 add() set1.add() 向 set1 集合中添加数字、字符串、元组或者布尔类型 >>> set1 = {1,2,3}
>>> set1.add((1,2))
>>> set1
{(1, 2), 1, 2, 3} clear() set1.clear() 清空 set1 集合中所有元素 >>> set1 = {1,2,3}
>>> set1.clear()
>>> set1
set()

set()才表示空集合，{}表示的是空字典 copy() set2 = set1.copy() 拷贝 set1 集合给 set2 >>> set1 = {1,2,3}
>>> set2 = set1.copy()
>>> set1.add(4)
>>> set1
{1, 2, 3, 4}
>>> set1
{1, 2, 3} difference()  set3 = set1.difference(set2) 将 set1 中有而 set2 没有的元素给 set3 >>> set1 = {1,2,3}
>>> set2 = {3,4}
>>> set3 = set1.difference(set2)
>>> set3
{1, 2} difference_update() set1.difference_update(set2) 从 set1 中删除与 set2 相同的元素 >>> set1 = {1,2,3}
>>> set2 = {3,4}
>>> set1.difference_update(set2)
>>> set1
{1, 2} discard() set1.discard(elem) 删除 set1 中的 elem 元素 >>> set1 = {1,2,3}
>>> set1.discard(2)
>>> set1
{1, 3}
>>> set1.discard(4)
{1, 3} intersection() set3 = set1.intersection(set2) 取 set1 和 set2 的交集给 set3 >>> set1 = {1,2,3}
>>> set2 = {3,4}
>>> set3 = set1.intersection(set2)
>>> set3
{3} intersection_update() set1.intersection_update(set2) 取 set1和 set2 的交集，并更新给 set1 >>> set1 = {1,2,3}
>>> set2 = {3,4}
>>> set1.intersection_update(set2)
>>> set1
{3} isdisjoint() set1.isdisjoint(set2) 判断 set1 和 set2 是否没有交集，有交集返回 False；没有交集返回 True >>> set1 = {1,2,3}
>>> set2 = {3,4}
>>> set1.isdisjoint(set2)
False issubset() set1.issubset(set2) 判断 set1 是否是 set2 的子集 >>> set1 = {1,2,3}
>>> set2 = {1,2}
>>> set1.issubset(set2)
False issuperset() set1.issuperset(set2) 判断 set2 是否是 set1 的子集 >>> set1 = {1,2,3}
>>> set2 = {1,2}
>>> set1.issuperset(set2)
True pop() a = set1.pop() 取 set1 中一个元素，并赋值给 a >>> set1 = {1,2,3}
>>> a = set1.pop()
>>> set1
{2,3}
>>> a
1 remove() set1.remove(elem) 移除 set1 中的 elem 元素 >>> set1 = {1,2,3}
>>> set1.remove(2)
>>> set1
{1, 3}
>>> set1.remove(4)
Traceback (most recent call last):
  File "<pyshell#90>", line 1, in <module>
    set1.remove(4)
KeyError: 4 symmetric_difference() set3 = set1.symmetric_difference(set2) 取 set1 和 set2 中互不相同的元素，给 set3 >>> set1 = {1,2,3}
>>> set2 = {3,4}
>>> set3 = set1.symmetric_difference(set2)
>>> set3
{1, 2, 4} symmetric_difference_update() set1.symmetric_difference_update(set2) 取 set1 和 set2 中互不相同的元素，并更新给 set1 >>> set1 = {1,2,3}
>>> set2 = {3,4}
>>> set1.symmetric_difference_update(set2)
>>> set1
{1, 2, 4} union() set3 = set1.union(set2) 取 set1 和 set2 的并集，赋给 set3 >>> set1 = {1,2,3}
>>> set2 = {3,4}
>>> set3=set1.union(set2)
>>> set3
{1, 2, 3, 4} update() set1.update(elem) 添加列表或集合中的元素到 set1 >>> set1 = {1,2,3}
>>> set1.update([3,4])
>>> set1
{1,2,3,4}