set和dict

爱被打了一巴掌 2021-11-11 15:36 301阅读 0赞

## dict属于mapping类型 ##

from collections.abc import Mapping,MutableMapping
    from collections.abc import __all__
    
    # dict 属于Mapping类型
    
    a = {}
    print(isinstance(a,MutableMapping))

## copy 浅拷贝 ##

a = {
        "liming1":{
        "company":"tencent1"},
        "liming2":{
        "company":"tencent2"},
    }
    
    # clear
    """ D.clear() -> None.  Remove all items from D. """
    # a.clear()
    
    #copy 浅拷贝
    """ D.copy() -> a shallow copy of D """
    new_dict = a.copy()
    new_dict['liming1']['company'] = 'tencent3'
    
    print(a)
    print(new_dict)
    
    ###########
    {
        'liming1': {
        'company': 'tencent3'}, 'liming2': {
        'company': 'tencent2'}}
    {
         'liming1': {
        'company': 'tencent3'}, 'liming2': {
        'company': 'tencent2'}}

## fromkeys ##

# fromkeys
    new_list = ['liming1','liming2']
    
    new_dict = dict.fromkeys(new_list,{
        'company':'tencent'})
    
    print(new_dict)

## update ##

# update
    
    new_dict.update({
         'lisa':{
        "company":"tencent2"}})
    new_dict.update({
         'liming2':{
        "company":"tencent2"}})
    new_dict.update(jenny={
        'company':'beijing'})
    new_dict.update([('jenny',{
        'company':'shanghai'})])
    print(new_dict)

## defaultdict   ##

__missing__ 很重要

from collections import defaultdict
    import collections
    s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
    
    d = collections.defaultdict(list)
    for k, v in s:
        d[k].append(v)
    
    print(list(d.items()))
    
    s = 'mississippi'
    d = defaultdict(int)
    for k in s:
         d[k] += 1
    print(list(d.items()))#set 不可变集合 fronzenset  无序  不重复

--------------------

## set和frozenset 的区别 ##

刚开始也讲了frozenset是不可变的，如果修改是报错的，那到底有什么用处呢  
应用场景：一般dict 的key 是不变的，我们就可以用  
那我们用代码证明下，set不会报错，frozenset 会报错.

s = {
        'a','b'}
    s.add('c')
    print(s)
    
    f = frozenset('abcd')  # 可以作为dict的key
    print(f)
    
    # 向set添加数据
    another_set = set('fgh')
    
    s.update(another_set)
    print(s)

## *difference 的用法*    ##

# 先看方法描述吧 （ Return the difference of two or more sets as a new set.）
    # 用例子加深印象。

a=set("abc")
    print(a.difference("bcd"))
    print(a)

## *set集合运算（|，&，-）* ##

a=set("abc")
    b=set("bcd")
    print(a-b)   #对a进行去重
    print(a | b) #并集
    print(a & b) #交集
    
    # {'a'}
    # {'c', 'a', 'd', 'b'}
    # {'c', 'b'}

转载于:https://www.cnblogs.com/richiewlq/p/11073272.html