Python string search operation
1.count function, return the number of repeated strings in the parameter (no overlap)
2.find () find the first place where the parameter string appears from the left, if not, return -1
3.rfind () find the first time from the right Where there is a parameter string, if not, return -1
4. startwith () to determine whether the string begins with the parameter string, yes, return true, otherwise return false
5.endswith () to determine whether the string ends with the parameter string, Yes, return true, otherwise return false
