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

　　　　|,|=: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