Question

The following is for Python 3.2.3.

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I would like to write a function that takes two arguments, a key string and a target string. These function is to recursively determine (it must be recursive) the positions of the key string in the target string.

Currently, my code is as follows.

def posSubStringMatchRecursive(target,key):
    import string
    index=str.rfind(target, key)
    if index !=-1:
        print (index)
        target=target[:(index+len(key)-1)]
        posSubStringMatchRecursive(target,key)

The issue with this is that there is no way to store all the locations of the key string in the target string in a list as the numbers indicating the location will just be printed out.

So, my question is, is there any way to change the code such that the positions of the key string in the target string can be stored in a list?

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Example Output

countSubStringMatchRecursive ('aatcgdaaaggraaa', 'aa')

13
12
7
6
0

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Edit

The following code seems to work without the issue in Ashwini’s code. Thanks, Lev.

def posSubStringMatchRecursive(target,key):
    import string
    index=str.rfind(target, key)
    if index ==-1:
        return []
    else:
        target=target[:(index+len(key)-1)]
        return ([index] + posSubStringMatchRecursive(target,key))

Answer 1

def posSubStringMatchRecursive(target,key,res):
    import string
    index=str.rfind(target, key)
    if index !=-1:

        target=target[:(index+len(key)-1)]
        res.append(index) #append the index to the list res, 
        return posSubStringMatchRecursive(target,key,res) #Use return here when calling recursively else your program will return None, and also pass res to the function
    else:
        return res

 print(posSubStringMatchRecursive('aatcgdaaaggraaa', 'aa',[]))#pass a empty list to the function
print(posSubStringMatchRecursive('aatcgdaaaggraaa', 'a',[]))

output:`

[13, 12, 7, 6, 0]`
[14, 13, 12, 8, 7, 6, 1, 0]