python字符串操作，以及截取对应的C#函数

inx = str.find("aa")

var inx = str.IndexOf("aa");

inx  = str.rfind("aa")

var inx = str.LastIndexOf("aa");

str = "asdfg"
str = str[3:]
#fg

var str = "asdfg";
str = str.Remove(0, 3);
//fg

str = "asdfg"
str = str[:3]
#asd

var str = "asdfg";
str = str.Remove(str.Length-2, 2);
//asd

str = "asdfg"
str = str[1:3]
#sd

var str = "asdfg";
str = str.Substring(1, 2);
//sd