Find index of last occurrence of a substring in a string

Question

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?

Answer 1

Use .rfind():

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

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

Answer 2

You can use rfind() or rindex()
^{Python2 links: rfind() rindex()}

>>> s = 'Hello StackOverflow Hi everybody'  >>> print( s.rfind('H') ) 20  >>> print( s.rindex('H') ) 20  >>> print( s.rfind('other') ) -1  >>> print( s.rindex('other') ) Traceback (most recent call last):   File "<stdin>", line 1, in <module> ValueError: substring not found 

The difference is when the substring is not found, rfind() returns -1 while rindex() raises an exception ValueError (Python2 link: ValueError).

If you do not want to check the rfind() return code -1, you may prefer rindex() that will provide an understandable error message. Else you may search for minutes where the unexpected value -1 is coming from within your code...

---

Example: Search of last newline character

>>> txt = '''first line ... second line ... third line'''  >>> txt.rfind('\n') 22  >>> txt.rindex('\n') 22