python学习笔记_集合的定义和常用方法

1、认识集合

定义：

s={1,2,3,4,5}

s=set("hello")

s=set(["steven","job","dave"])

用set和可迭代对象进行定义时，相当于执行了for循环

补充：集合属于可变类型，如果定义不可变类型的集合用frozenset(),

如s=frozenset("hello")

print(s)  #结果为：frozenset({'h', 'o', 'l', 'e'})

特点：

不同元素组成

无序

集合中的元素必须是不可变  （字符串，数字，元祖）

2、常用方法

.add("a")    #增加一个元素

.clear()      #清空

.copy()      #浅拷贝

.pop()       #随机删

.remove("job")       #指定删，删除元素不存在时会报错

.discard("job")       #指定删，删除元素不存在时不会报错

3、基本运算

交集，并集，差集

a_s={"steve","job","dave","max"}
b_s={"job","dave","mark"}
print(a_s,b_s)

#求交集
print(a_s.intersection(b_s))        #写法1
print(a_s&b_s)                      #写法2

#求并集
print(a_s.union(b_s))               #写法1
print(a_s|b_s)                      #写法2

#求差集,相当于存在于左边，但不存在于右边的集合
print(a_s.difference(b_s))          #写法1
print(a_s-b_s)                      #写法2
print(b_s-a_s)

结果：

{'dave', 'steve', 'max', 'job'} {'dave', 'mark', 'job'}
{'dave', 'job'}
{'dave', 'job'}
{'job', 'dave', 'mark', 'steve', 'max'}
{'job', 'dave', 'mark', 'steve', 'max'}
{'steve', 'max'}
{'steve', 'max'}
{'mark'}

4、其他方法

a_s={"steve","job","dave","max"}
b_s={"job","dave","mark"}
c_s={"job","dave"}

#交叉补集 ，交集的补集，相当于并集减去交集的部分的集合
print(a_s.symmetric_difference(b_s))    #写法1
print(a_s^b_s)                          #写法2
#结果为：{'mark', 'max', 'steve'}

#.difference_update()
a_s.difference_update(b_s)    # 相当于 a_s=a_s-b_s
print(a_s)
#结果为：{'max', 'steve'}

#.isdisjoint()  判断有没有交集，没有交集返回true
print(a_s.isdisjoint(b_s))
#结果为：false

#.issubset()  是否是某个集合的子集。相当于是s1<=s2
print(c_s.issubset(a_s))      #写法1
print(c_s<=a_s)               #写法2
#.issuperset() 是否是某个集合的父集。相当于是s1>=s2
print(a_s.issuperset(c_s))
#结果为 true

#.update() 可以增加多个值。可以传元祖，列表等可迭代对象
a_s.update(b_s)
print(a_s)
b_s.update(("bob","zhou"))
print(b_s)
#结果为：
#{'steve', 'job', 'max', 'dave', 'mark'}
#{'bob', 'mark', 'job', 'dave', 'zhou'}

"""
    set() -> new empty set object
    set(iterable) -> new set object

    Build an unordered collection of unique elements.
    """
    def add(self, *args, **kwargs): # real signature unknown
        """
        Add an element to a set.

        This has no effect if the element is already present.
        """
        pass

    def clear(self, *args, **kwargs): # real signature unknown
        """ Remove all elements from this set. """
        pass

    def copy(self, *args, **kwargs): # real signature unknown
        """ Return a shallow copy of a set. """
        pass

    def difference(self, *args, **kwargs): # real signature unknown
        """
        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.)
        """
        pass

    def difference_update(self, *args, **kwargs): # real signature unknown
        """ Remove all elements of another set from this set. """
        pass

    def discard(self, *args, **kwargs): # real signature unknown
        """
        Remove an element from a set if it is a member.

        If the element is not a member, do nothing.
        """
        pass

    def intersection(self, *args, **kwargs): # real signature unknown
        """
        Return the intersection of two sets as a new set.

        (i.e. all elements that are in both sets.)
        """
        pass

    def intersection_update(self, *args, **kwargs): # real signature unknown
        """ Update a set with the intersection of itself and another. """
        pass

    def isdisjoint(self, *args, **kwargs): # real signature unknown
        """ Return True if two sets have a null intersection. """
        pass

    def issubset(self, *args, **kwargs): # real signature unknown
        """ Report whether another set contains this set. """
        pass

    def issuperset(self, *args, **kwargs): # real signature unknown
        """ Report whether this set contains another set. """
        pass

    def pop(self, *args, **kwargs): # real signature unknown
        """
        Remove and return an arbitrary set element.
        Raises KeyError if the set is empty.
        """
        pass

    def remove(self, *args, **kwargs): # real signature unknown
        """
        Remove an element from a set; it must be a member.

        If the element is not a member, raise a KeyError.
        """
        pass

    def symmetric_difference(self, *args, **kwargs): # real signature unknown
        """
        Return the symmetric difference of two sets as a new set.

        (i.e. all elements that are in exactly one of the sets.)
        """
        pass

    def symmetric_difference_update(self, *args, **kwargs): # real signature unknown
        """ Update a set with the symmetric difference of itself and another. """
        pass

    def union(self, *args, **kwargs): # real signature unknown
        """
        Return the union of sets as a new set.

        (i.e. all elements that are in either set.)
        """
        pass

    def update(self, *args, **kwargs): # real signature unknown
        """ Update a set with the union of itself and others. """
        passseset

set