12.5、python基础数据类型(set集合)-阿里云开发者社区

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12.5、python基础数据类型(set集合)

简介: 基础数据类型(set集合) 认识集合   由一个或多个确定的元素所构成的整体叫做集合。   集合中的元素有三个特征:     1.确定性(集合中的元素必须是确定的)     2.互异性(集合中的元素互不相同。

基础数据类型(set集合)

认识集合

  由一个或多个确定的元素所构成的整体叫做集合。

  集合中的元素有三个特征:

    1.确定性(集合中的元素必须是确定的)

    2.互异性(集合中的元素互不相同。例如:集合A={1,a},则a不能等于1)

    3.无序性(集合中的元素没有先后之分),如集合{3,4,5}和{3,5,4}算作同一个集合。

  *集合概念存在的目的是将不同的值存放到一起,不同的集合间用来做关系运算,无需纠结于集合中某个值

集合的定义

  s = {1,2,3,1}

#定义可变集合>>> set_test=set('hello')

>>> set_test

{'l', 'o', 'e', 'h'}#改为不可变集合frozenset>>> f_set_test=frozenset(set_test)

>>> f_set_test

frozenset({'l', 'e', 'h', 'o'})

集合的常用操作及关系运算

  元素的增加

  单个元素的增加 : add(),add的作用类似列表中的append

  对序列的增加 : update(),而update类似extend方法,update方法可以支持同时传入多个参数:

>>> a={1,2}

>>> a.update([3,4],[1,2,7])

>>> a

{1, 2, 3, 4, 7}

>>> a.update("hello")

>>> a

{1, 2, 3, 4, 7, 'h', 'e', 'l', 'o'}

>>> a.add("hello")

>>> a

{1, 2, 3, 4, 'hello', 7, 'h', 'e', 'l', 'o'}

  元素的删除

  集合删除单个元素有两种方法:

    元素不在原集合中时:

      set.discard(x)不会抛出异常

      set.remove(x)会抛出KeyError错误

>>> a={1,2,3,4}

>>> a.discard(1)

>>> a

{2, 3, 4}

>>> a.discard(1)

>>> a

{2, 3, 4}

>>> a.remove(1)

Traceback (most recent call last):

  File "<input>", line 1, in <module>

KeyError: 1

  pop():由于集合是无序的,pop返回的结果不能确定,且当集合为空时调用pop会抛出KeyError错误,

  clear():清空集合

>>> a={3,"a",2.1,1}

>>> a.pop()

1

>>> a.pop()

3

>>> a.clear()

>>> a

set()

>>> a.pop()

Traceback (most recent call last):

  File "<input>", line 1, in <module>

KeyError: 'pop from an empty set'

  集合操作


img_b6015fdc0679f768d95104ffd6fd18ff.jpe

    |,|=:合集

a = {1,2,3}

b = {2,3,4,5}print(a.union(b))print(a|b)

    &.&=:交集

a = {1,2,3}

b = {2,3,4,5}print(a.intersection(b))print(a&b)

    -,-=:差集

a = {1,2,3}

b = {2,3,4,5}print(a.difference(b))print(a-b) 

    ^,^=:对称差集

a = {1,2,3}

b = {2,3,4,5}print(a.symmetric_difference(b))print(a^b)


  包含关系

    in,not in:判断某元素是否在集合内

    ==,!=:判断两个集合是否相等

    两个集合之间一般有三种关系,相交、包含、不相交。在Python中分别用下面的方法判断:

set.isdisjoint(s):判断两个集合是不是不相交

set.issuperset(s):判断集合是不是包含其他集合,等同于a>=b

set.issubset(s):判断集合是不是被其他集合包含,等同于a<=b

集合的工厂函数

class set(object):

    """

    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        """

        相当于s1-s2


        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        """

        与remove功能相同,删除元素不存在时不会抛出异常


        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        """

        相当于s1&s2


        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        """

        相当于s1<=s2


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

        相当于s1>=s2


        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        """

        相当于s1^s2


        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        """

        相当于s1|s2


        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. """        pass    def __and__(self, *args, **kwargs): # real signature unknown        """ Return self&value. """        pass    def __contains__(self, y): # real signature unknown; restored from __doc__        """ x.__contains__(y) <==> y in x. """        pass    def __eq__(self, *args, **kwargs): # real signature unknown        """ Return self==value. """        pass    def __getattribute__(self, *args, **kwargs): # real signature unknown        """ Return getattr(self, name). """        pass    def __ge__(self, *args, **kwargs): # real signature unknown        """ Return self>=value. """        pass    def __gt__(self, *args, **kwargs): # real signature unknown        """ Return self>value. """        pass    def __iand__(self, *args, **kwargs): # real signature unknown        """ Return self&=value. """        pass    def __init__(self, seq=()): # known special case of set.__init__        """

        set() -> new empty set object

        set(iterable) -> new set object


        Build an unordered collection of unique elements.

        # (copied from class doc)

        """        pass    def __ior__(self, *args, **kwargs): # real signature unknown        """ Return self|=value. """        pass    def __isub__(self, *args, **kwargs): # real signature unknown        """ Return self-=value. """        pass    def __iter__(self, *args, **kwargs): # real signature unknown        """ Implement iter(self). """        pass    def __ixor__(self, *args, **kwargs): # real signature unknown        """ Return self^=value. """        pass    def __len__(self, *args, **kwargs): # real signature unknown        """ Return len(self). """        pass    def __le__(self, *args, **kwargs): # real signature unknown        """ Return self<=value. """        pass    def __lt__(self, *args, **kwargs): # real signature unknown        """ Return self<value. """        pass    @staticmethod # known case of __new__    def __new__(*args, **kwargs): # real signature unknown        """ Create and return a new object.  See help(type) for accurate signature. """        pass    def __ne__(self, *args, **kwargs): # real signature unknown        """ Return self!=value. """        pass    def __or__(self, *args, **kwargs): # real signature unknown        """ Return self|value. """        pass    def __rand__(self, *args, **kwargs): # real signature unknown        """ Return value&self. """        pass    def __reduce__(self, *args, **kwargs): # real signature unknown        """ Return state information for pickling. """        pass    def __repr__(self, *args, **kwargs): # real signature unknown        """ Return repr(self). """        pass    def __ror__(self, *args, **kwargs): # real signature unknown        """ Return value|self. """        pass    def __rsub__(self, *args, **kwargs): # real signature unknown        """ Return value-self. """        pass    def __rxor__(self, *args, **kwargs): # real signature unknown        """ Return value^self. """        pass    def __sizeof__(self): # real signature unknown; restored from __doc__        """ S.__sizeof__() -> size of S in memory, in bytes """        pass    def __sub__(self, *args, **kwargs): # real signature unknown        """ Return self-value. """        pass    def __xor__(self, *args, **kwargs): # real signature unknown        """ Return self^value. """        pass    __hash__ = None

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