集合（set）是基本数据类型的一种集合类型，它有可变集合（set()）和不可变集合（frozenset()）两种。
集合的特点：
- 由不同元素组成
- 无序
- 集合中元素必须是不可变类型（number，string，tuple）
创建可变集合
s = {2, 3, 1, 4, 3}
print(s) # {1, 2, 3, 4}
# 通过set()创建
s = set('hello')
print(s) # {'e', 'o', 'l', 'h'}
s = set(['xiao', 'xiao', 'ming'])
print(s) # {'xiao', 'ming'}
集合内置方法
add() # 添加
s = {1, 2, 3}
s.add('xm')
print(s) # {1, 2, 3, 'xm'}
s.add(3)
print(s) # {1, 2, 3, 'xm'}
clear() # 清空
s = {1, 3, 2}
s.clear()
print(s) # set()
pop() # 删除
s = {1, 2, 3, 'xm'}
s.pop()
print(s) # {2, 3, 'xm'}
remove() # 指定删除，删除不存在的元素会报错
s = {1, 2, 3, 'xm'}
s.remove('xm')
print(s) # {1, 2, 3}
s.remove('xxm') # 报错
discard() # 指定删除，删除不存在的元素不会报错
s = {1, 2, 3, 'xm'}
s.discard('xm')
print(s) # {1, 2, 3}
s.discard('xxm') # 不会报错，继续执行下面的代码
print(s) # {1, 2, 3}
copy() # 拷贝（复制）
s = {1, 2, 3, 'xm'}
new_s = s.copy()
print(new_s) # {1, 2, 3, 'xm'}
update() # 更新
s1 = {1, 2, 3, 'xm'}
s1.update('enen') # 字符串
print(s1) # {1, 2, 3, 'xm', 'n', 'e'}
s1.update({3, 4, 'enen'}) # 集合
print(s1) # {1, 2, 3, 4, 'e', 'enen', 'n', 'xm'}
s1.update(('abc', 'qwe')) # 元组
print(s1) # {1, 2, 3, 4, 'abc', 'e', 'enen', 'qwe', 'n', 'xm'}
s1.update(['list1', 'list2']) # 列表
print(s1) # {1, 2, 3, 4, 'abc', 'list1', 'list2', 'e', 'enen', 'qwe', 'n', 'xm'}
集合交、差、并集
intersection() # 交集（&）
# 语法 # set1.intersection(set2) py_list = {'ergou', 'xiaoming', 'goudan'} php_list = {'xiaoming', 'xiaohong','xiaosan'} print(py_list.intersection(php_list)) # {'xiaoming'} print(py_list & php_list) # {'xiaoming'}
union() # 并集（|）
# 语法 # set1.union(set2) py_list = {'ergou', 'xiaoming', 'goudan'} php_list = {'xiaoming', 'xiaohong','xiaosan'} print(py_list.union(php_list)) # {'ergou', 'xiaoming', 'goudan', 'xiaohong', 'xiaosan'} print(py_list | php_list) # {'ergou', 'xiaoming', 'goudan', 'xiaohong', 'xiaosan'}
difference() # 差集（-）
# 语法 # set1.difference(set2) py_list = {'ergou', 'xiaoming', 'goudan'} php_list = {'xiaoming', 'xiaohong','xiaosan'} print(py_list.difference(php_list)) # {'ergou', 'goudan'} print(php_list.difference(py_list)) # {'xiaohong', 'xiaosan'} print(py_list - php_list) # {'ergou', 'goudan'} print(php_list - py_list) # {'xiaohong', 'xiaosan'}
symmetric_difference() # 交叉补集（^）
# 语法 # set1.symmetric_difference(set2) py_list = {'ergou', 'xiaoming', 'goudan'} php_list = {'xiaoming', 'xiaohong','xiaosan'} print(py_list.symmetric_difference(php_list)) # {'ergou', 'goudan', 'xiaohong', 'xiaosan'} print(py_list ^ php_list) # {'ergou', 'goudan', 'xiaohong', 'xiaosan'}
difference_update() #
# 相当于 # set1 = set1 - set2 py_list = {'ergou', 'xiaoming', 'goudan'} php_list = {'xiaoming', 'xiaohong','xiaosan'} print(py_list.difference_update(php_list)) # {'ergou', 'goudan'} print(php_list.difference_update(py_list)) # {'xiaohong', 'xiaosan'}
intersection_update() #
# 相当于 # set1 = set1 & set2 py_list = {'ergou', 'xiaoming', 'goudan'} php_list = {'xiaoming', 'xiaohong','xiaosan'} py_list.intersection(php_list) print(py_list) # {'xiaoming'}
indisjoint() # 判断两集合交集是否为空（没有交集返回->True，有交集返回->False）
# 格式 # set1.isdisjoint(set2) s1 = {1, 2, 3} s2 = {4, 5, 6} var = s1.isdisjoint(s2) print(var) # True s2 = {3, 4, 5} var = s1.isdisjoint(s2) print(var) # False
issubset() # 判断一个集合是否是另一个集合的子集
# set1.issubset(s2) s1 = {1, 2, 3} s2 = {1, 2, 3, 4, 5, 6} print(s1.issubset(s2)) # True print(s2.issubset(s1)) # False
issuperset() # 判断一个集合是否是另一个集合的父集
# set1.issuperset(s2) s1 = {1, 2, 3} s2 = {1, 2, 3, 4, 5, 6} print(s1.issubset(s2)) # False print(s2.issubset(s1)) # True
symmetric_difference_update() #
# 相当于 # set1 = set1.symmetric_difference(set2) s1 = {1, 2, 3} s2 = {3, 4, 5} s1.symmetric_difference_update(s2) print(s1) # {1, 2, 4, 5}
创建不可变集合
s = frozenset('xiaoming') print(s) # frozenset({'m', 'g', 'o', 'a', 'i', 'x', 'n'})