Definition: A substring is a sequence of contiguous symbols within a string. For example: $$ana$$ is a substring of $$banana$,$ and $$umber$$ is a substring of $$cucumber$.$ Every string is a substring of itself.

Python provides us a handy method for counting substrings within a string: $.$count$().$ For example, the word $$understandable$$ contains two occurrences of the substring $$nd$$:

$>>>$ "understandable".count$("$nd$")$

$2$

$>>>$

However, $.$count$()$ doesn$$t handle overlapping substrings well. For example, the word $$banana$$ contains two overlapping occurrences of the substring $$ana$,$ but $.$count$()$ only counts one:

$>>>$ "banana".count$("$ana$")$

$1$

$>>>$

You are to write a function which counts occurrences of a substring within a string, including overlapping occurrences. So$,$ for example, if the input to the function is $$banana$,$ the function should return $2.$ We can look for other overlapping substrings in any arbitrary string. For example, in the string $$gactactaggacta$$ has three occurrences of the substring $$acta$($where two overlap$).$ Notice also that a single letter is also a substring, so $$gactactaggacta$$ contains $5$ occurrences of the substring $$a$.$

The program

Write a program which prompts the user for a string and a substring and then reports the number of occurrences of the substring within the string, overlapping or otherwise. Examples of separate runs of such a program:

Enter a string: gactactaggacta

Enter a substring: acta

$3$

Enter a string: gactactaggacta

Enter a substring: a

$5$

Enter a string: gactactaggacta

Enter a substring: tag

$1$

Enter a string: gactactaggacta

Enter a substring: porcupine

$0$

For this you should write a function substring$\_$count$().$ This function should take two arguments: the first argument should be the string to be searched, and the second argument should be the substring. This function should return an int, the number of occurrences found. This function should return $0$ if the substring is not found or if the substring is the empty string.

You should implement this function without the use of any string methods, e$.$g$.,.$count$(),.$split$(),.$index$(),.$find$(),$ etc. None of these is needed to solve the problem. The goal is to work with the elements of the string directly, using iteration and indexed reads.