Python - Check if string repeats itself

Checking if a string repeats itself means determining whether the string consists of multiple repetitions of a smaller substring.

Using slicing and multiplication

We can check if the string is a repetition of a substring by slicing and reconstructing the string using multiplication.

s = "ababab"
# Check if string repeats by slicing and multiplying
res = s in (s + s)[1:-1]
print(res)  

True

Explanation:

• We concatenate the string with itself to allow rotation-based checks.
• We remove the first and last characters of the concatenated string.
• If the original string exists in this modified string, it means it is made up of repeated substrings.

Let's explore some more methods and see how we can check if string repeats itself in python.

Using regular expressions

We can use a regular expression to check for a repeating pattern.

import re
s = "ababab"
# Check for repeating pattern using regex
res = bool(re.fullmatch(r"(.+)\1+", s))
print(res)  

True

Explanation:

• The regular expression (.+)\1+ checks for one or more occurrences of a substring followed by itself.
• If the string matches this pattern, it repeats itself.

Using for loop

We can manually iterate through the string using a for loop to find the smallest substring that repeats to form the entire string.

s = "ababab"
# Initialize result as False
res = False
# Iterate through possible lengths of substrings
for i in range(1, len(s) // 2 + 1):
    # Check if current length divides the string evenly
    if len(s) % i == 0:
        # Check if the substring repeats to form the string
        if s[:i] * (len(s) // i) == s:
            res = True
            break
print(res)  

True

Explanation:

• We iterate through all possible lengths of substrings up to half the length of the string.
• If the substring repeats to match the entire string, we set the result to True.

Using concatenation

Another simple method involves using find() function after concatenating the string with itself.

s = "ababab"
# Check for repeating pattern using string concatenation
res = (s + s).find(s, 1) != len(s)
print(res)  

True

Explanation:

• We concatenate the string with itself and check if the original string appears again, starting from the second character.
• If it does, the string is made of repeated substrings.

Using string slicing and comparison

We can use slicing and comparison to check for a repeating pattern by dividing the string into smaller parts.

s = "ababab"
# Assume no repetition initially
res = False
# Check for repeating pattern by slicing
for i in range(1, len(s)):
    if len(s) % i == 0 and s[:i] * (len(s) // i) == s:
        res = True
        break
print(res)  

True

Explanation:

• We divide the string into smaller slices and check if they form the entire string through repetition.