Python - Get all substrings of given string

A substring is any contiguous sequence of characters within the string. We'll discuss various methods to extract this substring from a given string by using a simple approach.

Using List Comprehension :

List comprehension offers a concise way to create lists by applying an expression to each element in an iterable. It enables efficient operations like counting characters in a string in a single line of code

s = "abc"

# Generate all substrings using list comprehension
substrings = [s[i:j] for i in range(len(s)) for j in range(i+1, len(s)+1)]

# Print the result
print(substrings)  

['a', 'ab', 'abc', 'b', 'bc', 'c']

Explanation:

• Generate substrings using list comprehension: A nested list comprehension is used to create all possible substrings by iterating through all starting (i) and ending (j) indices in the string.
• Print the result: The resulting list substrings contains all substrings of the string s, and it is printed.

Let's explore various other methods to Get all substrings of a given strings:

Using Nested Loops:

Nested loops in Python allow you to iterate over multiple levels of data, making them useful for tasks like generating substrings. By using a loop inside another loop, you can access each combination of starting and ending indices in a string to extract all substrings.

s = "abc"

# Initialize a list to store substrings
substrings = []

# Use nested loops to generate substrings
for i in range(len(s)):
    for j in range(i + 1, len(s) + 1):
        substrings.append(s[i:j])

print(substrings) 

['a', 'ab', 'abc', 'b', 'bc', 'c']

Explanation:

• Generate substrings using nested loops: Two loops are used to iterate through all possible starting (i) and ending (j) indices of the string, extracting the substrings with text[i:j].
• Store and print the result: Each generated substring is appended to the substrings list, and the final list is printed.

Using slice()

slice notation in Python allows you to extract a portion of a string by specifying a start, stop, and optional step. It provides a simple and efficient way to generate substrings by accessing specific ranges of indices directly.

s = "abc"

# Initialize a list to store substrings
substrings = []

# Use slice() to generate all substrings
for i in range(len(s)):
    for j in range(i + 1, len(s) + 1):
        substrings.append(s[slice(i, j)])


print(substrings)  

['a', 'ab', 'abc', 'b', 'bc', 'c']

Explanation

• Generate substrings using slice(): Two nested loops iterate through all possible starting (i) and ending (j) indices, and the slice() function is used to extract substrings from the string using these indices.
• Store substrings in a list: Each generated substring is appended to the substrings list for collection.

Using itertools.combinations():

itertools.combinations() function generates all possible combinations of a given length from an iterable. It is useful for generating substrings of a specific length by specifying the range of indices for each combination.

import itertools

# Define the input string
s = "abc"

# Get all substrings using combinations of indices
substrings = [''.join(s[i:j]) for i, j in itertools.combinations(range(len(s) + 1), 2)]

print(substrings)  

['a', 'ab', 'abc', 'b', 'bc', 'c']

Explanation

• Generate combinations of indices: The itertools.combinations() function generates all pairs of indices (i, j) from the range of indices of the string, which are used to define the start and end points of each substring.
• Create substrings: For each pair of indices, the text[i:j] slices the string, and the substrings are collected in a list using list comprehension.