python学习第三天-集合

增：

　　add

a = {1,2,3}
a.add(4)
print(a)
#{1, 2, 3, 4}

删：

　　discard、remove、pop

a = {1,2,3}
a.remove(1)
print(a)
a.discard(1)
print(a)
a.discard(2)
print(a)
#{2, 3}
#{2, 3}
#{3}

改(不支持，也不支持切片，无索引)：

a = {1,2,3}
print(a[0])
# File "E:/pythondir/Day01/task02.py", line 2, in <module>
    print(a[0])
TypeError: 'set' object is not subscriptable

查：

　　in or not in 

并集：

　　| 、union

a = {1,2,3,4,5}
b = {2,3,5,6,7,8,9}
print(a | b)
print(a.union(b))
#{1, 2, 3, 4, 5, 6, 7, 8, 9}
#{1, 2, 3, 4, 5, 6, 7, 8, 9}

差集：

　-、difference　

a = {1,2,3,4,5}
b = {2,3,5,6,7,8,9}
print(a - b)
print(a.difference(b))
print(a.difference_update(b))  #去掉交集,并更新
print(a)
#{1, 4}
#{1, 4}
#None
#{1, 4}

交集：

　　&、intersection

a = {1,2,3,4,5}
b = {2,3,5,6,7,8,9}
print(a & b)
print(a.intersection(b))
#{2, 3, 5}
#{2, 3, 5}

对称差集（两者并集去掉交集）：

　　^、symmetric_difference

a = {1,2,3,4,5}
b = {2,3,5,6,7,8,9}
print(a ^ b)
print(a.symmetric_difference(b))
#{1, 4, 6, 7, 8, 9}
#{1, 4, 6, 7, 8, 9}