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Strings can be reversed using slicing. To reverse a string, we simply create a slice that starts with the length of the string, and ends at index 0. The slice statement means start at string length, end at position 0, move with the step -1 (or one step backward).
The rfind() method finds the last occurrence of the specified value. The rfind() method returns -1 if the value is not found.
Python provides different ways and methods to generate a substring, to check if a substring is present, to get the index of a substring, and more. start - The starting index of the substring. stop - The final index of a substring. step - A number specifying the step of the slicing.
Your call tell rfind to start looking at index 34. You want to use the rfind overload that takes a string, a start and an end. Tell it to start at the beginning of the string (0) and stop looking at index:
>>> s = "Hello, I am 12! I like plankton but I don't like Baseball."
>>> index = 34 #points to the 't' in 'but'
>>> index_of_2nd_I = s.rfind('I', 0, index)
>>>
>>> index_of_2nd_I
16
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)
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