Find index of last occurrence of a substring in a string

I want to find the position (or index) of the last occurrence of a certain substring in given input string str.

For example, suppose the input string is str="hello" and the substring is target="l", then it should output 3.

How can I do this?

Use .rfind():

>>> s="hello"
>>> s.rfind('l')
3

Also don’t use str as variable name or you’ll shadow the built-in str().