python字符串方法之查找

Posted 2020-09-15

str.find()

str.rfind()

【作用：类似index，查找字符】

【英语：r=》right|右边，find=》寻找】

【说明：返回一个新的整数，查找到的位置，找不到出现-1，index找不到要报错】

In [190]:  "The stars are not afraid to appear like fireflies.".find("vition")#不存在返回-1
Out[190]: -1
In [192]:  "The stars are not afraid to appear like fireflies.".find("a")#从左边开始查找
Out[192]: 6
In [193]:  "The stars are not afraid to appear like fireflies.".rfind("a")#从右边开始查找
Out[193]: 32

str.count(sub[,start[,end]])

【作用：统计指定字符在字符串中出现的次数，可以根据起始和结束位置来统计】

【英语：count=>统计，case=》情况】

【说明：返回统计到的数量】

In [79]: "Man is a born child, his power is the power of growth. ".count("o")#从整个字符串中统计‘o’出现的次数
Out[79]: 5
In [80]: "Man is a born child, his power is the power of growth. ".count("o",0,11)#从位置0到11统计‘o’出现的次数
Out[80]: 1

str.index(sub[,start[,end]])

str.rindex(sub[,start[,end]])

【作用：从字符串左边开始查找，sub=》要查找的子字符串，start=》开始的位置，从0开始，end=>结束的位置】

【英语：index=>索引，r=>right|右边】

【说明：返回查找的字符串在源字符串的位置，找不到会报错】

In [63]: "What you are you do not see".index("e")#默认从左边开始查找，
Out[63]: 11
In [43]: "What you are you do not see".rindex("e")#从右边开始查找，
Out[43]: 26
In [45]: "What you are you do not see".rindex("W",1)#从位置1开始并且从右边开始查找
结果报错
In [46]: "What you are you do not see".rindex("d",0,20))#从位置0到20中并且从右边开始查找
Out[46]: 17