Python之路 - 集合

介绍 🍀

集合是一个无序的 , 不重复的数据组合 , 它的主要作用如下 :

去重 , 把一个列表变成集合 , 就自动去重了
关系测试 , 测试两组数据之间的交集 , 差集 , 并集关系

在Python 2.7中集合表示如下 :

1	set([1,2,3])

在Python 3.x 中则是如下 :

s1 = {1,2,3,4}
print(s1)
print(type(s1))

>>> {1, 2, 3, 4}
<class 'set'>

集合支持一系列标准操作 , 包括并集 , 交集 , 差集 , 对称差集

创建 🍀

与字符串等数据类型一样 , 集合支持如下方式创建

# 创建空集合只能用这种方式,参数为一个可迭代对象
s = set()
# 注意集合是单个元素,字典是键值对
s = {1,2,3}

添加 🍀

为集合添加元素

# 定义集合
s = {'lyon','kenneth'}
# 添加一项
s.add('geek')

注意 : 集合不支持 “+”

更新 🍀

# 定义集合
s = {'lyon','kenneth'}
# 添加多项,参数为可迭代对象
s.update(['1','2','3'])

删除 🍀

# 定义集合
s = {'lyon','kenneth'}
# 删除一项
s.remove('kenneth')
# 清空集合
s.clear()

测试 🍀

a = {1,2,3,4,5}
b = {1,2,3}
# 测试是否b中的每一个元素都在a中,即 b<=a ,返回bool值
b.issubset(a)
# 测试是否a中的每一个元素都在b中,即 b>=a ,返回bool值
b.issuperset(a)

集合操作 🍀

>>>a = {1,2,3}
>>>b = {4,5,6}
# 求并集
>>>a.union(b)
# 同上,求并集
>>>a | b
# 求交集
>>>a.intersection(b)
# 同上,求交集
>>>a & b
# 求差集
>>>a.difference(b)
# 同上,求差集
>>>a - b
# 求对称差集
>>>a.symmetric_difference(b)
# 同上,求对称差集
>>>a ^ b

集合对象所有方法

|  add(...)
|      Add an element to a set.
|
|      This has no effect if the element is already present.
|
|  clear(...)
|      Remove all elements from this set.
|
|  copy(...)
|      Return a shallow copy of a set.
|
|  difference(...)
|      Return the difference of two or more sets as a new set.
|
|      (i.e. all elements that are in this set but not the others.)
|
|  difference_update(...)
|      Remove all elements of another set from this set.
|
|  discard(...)
|      Remove an element from a set if it is a member.
|
|      If the element is not a member, do nothing.
|
|  intersection(...)
|      Return the intersection of two sets as a new set.
|
|      (i.e. all elements that are in both sets.)
|
|  intersection_update(...)
|      Update a set with the intersection of itself and another.
|
|  isdisjoint(...)
|      Return True if two sets have a null intersection.
|
|  issubset(...)
|      Report whether another set contains this set.
|
|  issuperset(...)
|      Report whether this set contains another set.
|
|  pop(...)
|      Remove and return an arbitrary set element.
|      Raises KeyError if the set is empty.
|
|  remove(...)
|      Remove an element from a set; it must be a member.
|
|      If the element is not a member, raise a KeyError.
|
|  symmetric_difference(...)
|      Return the symmetric difference of two sets as a new set.
|
|      (i.e. all elements that are in exactly one of the sets.)
|
|  symmetric_difference_update(...)
|      Update a set with the symmetric difference of itself and another.
|
|  union(...)
|      Return the union of sets as a new set.
|
|      (i.e. all elements that are in either set.)
|
|  update(...)
|      Update a set with the union of itself and others.