Python 集合操作

集合 set

集合用于包含一组无序的对象
与列表和元组不同，集合是无序的，也无法通过数字进行索引。
集合中的元素不能重复
set和dict一样，只是没有value，相当于dict的key集合
由于dict的key是不重复的，且key是不可变对象因此set也有如下特性：

▷不重复，（互异性），也就是说集合是天生去重的
▷元素为不可变对象，（确定性，元素必须可hash）
▷集合的元素没有先后之分，（无序性）

python3.x集合的内置函数有17个

class set(object):
    """
    set() -> new empty set object
    set(iterable) -> new set object
    
    Build an unordered collection of unique elements.
    """

是把要传入的元素做为一个整个添加到集合中

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

清空集合里面的所有元素

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

复制集合里面的所有元素 ，返回一个浅复制

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

求两个集合里面的不同的元素 ，又称差

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

返回删除了 set “集合2”中含有的元素后的 set “集合1”

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

如果在 set “集合”中存在元素 x, 则删除

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

求两个集合里面相同的元素，又称并. 返回只保留含有 set “集合2”中元素的 set “集合1”

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

返回只保留含有 set “集合2”中元素的 set “集合1” ，并更新自己

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

判断两个集合是不是不相交，并返回

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

判断集合是不是包含其他集合，等同于a>=b

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

判断集合是不是被其他集合包含，等同于a<=b

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

删除并且返回 set “集合”中的一个不确定的元素, 如果为空则引发 KeyError

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

从 set “集合”中删除元素 , 如果不存在则引发 KeyError

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

返回一个新的 set 包含外面和里面中不重复的元素,也就是两个集合不重复的元素

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

返回含有 set “里面”或者 set “外面”中有而不是两者都有的元素的 set “外面”

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

把两个集合连接起来，又称并

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

把两个集合连接起来，又称并

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

1.定义集合

a1=[1,2,3,4]
print(set(a1))
>>> {1, 2, 3, 4}
#或者直接定义一个集合
a2_set={1,2,3,4,5}

2.增(更新)

set.add()
set.update([])
# set.add() 只能增加一个, 不能同时增加多个值
a1={1,2,3,4}
a1.add(8)
a1
>>> {1, 2, 3, 4, 8}
--------------------------------------
a1.add(11,12)    # 同时增加多个值报错
Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: add() takes exactly one argument (2 given)
--------------------------------------
""" Update a set with the union of itself and others. """
# a2 集合与 a1 集合 合并更新成为新的 a2 集合
a1={1,2,3,4}
a2={11,12,13}
a2.update(a1)
a2
>>> {1, 2, 3, 4, 8, 11, 12, 13}