python快速入门（5）字典结构

1.查找对应关系

下图中，student和score是一一对应的

注意score与scores的区分

names = ['cao','yue','edward','roy']scores = [90,91,92,93]indexes = [0,1,2,3]name = 'yue'score = 0for i in indexes:    if names[i] == name:        score = scores[i]print(score)

遍历了两个List，时间复杂度很高。python提供了字典，可以利用。

2.定义字典

利用大括号{}定义 

name = {}print(type(name))

3.字典的结构是Key和Value

比如定义scores[“Roy”] = 90

左边"Roy"是Key，右边90是Value

第一种方式定义字典：

name = {}name['cao'] = 100name['yue'] = 99print(name)print(name['cao'])

输出字典以及指定好key的value

第二种方式定义字典：

name = {    'cao':100,    'yue':99}print(name)print(type(name))

4.更改字典中的值

name = {    'cao':100,    'yue':99}name['cao'] = 101print(name)name['cao'] = name['cao'] +101print(name)

5.判断元素是否在字典中

name = {    'cao':100,    'yue':99}print('caos' in name)

6.用字典做list的计数

months = [1,2,1,4,5,7,8,25,3,54,5,1,4,5]month_count = {}for i in months:    if i in month_count:        month_count[i] += 1    else:        month_count[i] = 1print(month_count)