Python Reverse Find in String

Question

I have a string and an arbitrary index into the string. I want find the first occurrence of a substring before the index.

An example: I want to find the index of the

Answer 1

I became curious how to implement looking n times for string from end by rpartition and did this nth rpartition loop:

orig = s = "Hello, I am 12! I like plankton but I don't like Baseball."
found = tail = ''
nthlast = 2
lookfor = 'I'
for i in range(nthlast):
    tail = found+tail
    s,found,end = s.rpartition(lookfor)
    if not found:
        print "Only %i (less than %i) %r in \n%r" % (i, nthlast, lookfor, orig)
        break
    tail = end + tail
else:
    print(s,found,tail)