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 = 0 for 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'] = 100 name['yue'] = 99 print(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'] = 101 print(name) name['cao'] = name['cao'] +101 print(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] = 1 print(month_count)