Get All Substrings Of A String In Python

No built-in function only algorithm

The algorithm

Let’s say you want to find all possible substrings of a BANANA in Python. Hopefully, there is no built-in function for this, and we have to use our brains to develop an algorithm for it.

One way to achieve this is by setting two pointers, i at the beginning and j at the end of the string. We start off by decreasing j, and for every move, we take the slice of string[i:j] and add it to the list.

Once the pointers i and j intersect, we increase i and set j to the end of the string. We repeat this process until i reaches the end of the string’s length. The algorithm will look like the one below in Python:

def find_all_substrings(string):
   
    result = []
    i = 0
    j = len(string)
   
    while i != len(string)-1:
        substring = string[i:j]
        if substring not in result:
            result.append(substring)
        if j == i: 
            j = len(string)
            i += 1
        else:
            j-=1 
              
    return result
    
find_all_substrings("BANANA")

Output for BANANA:

['BANANA', 'BANAN', 'BANA', 'BAN', 'BA', 'B', 'ANANA', 'ANAN', 'ANA', 'AN', 'A', 'NANA', 'NAN', 'NA', 'N']