How to write Python Regular Expression find repeating digits in a number?

In this article, you will learn to write regular expressions in Python to find repeating digits in a given number. Regular expressions are a powerful feature that helps you find matching patterns in strings.

Finding repeating digits is useful in many areas like data validation, pattern recognition, and number analysis. For example, in the number 1223, we can identify that "22" contains repeating digits.

Understanding the Regex Pattern

To find repeating digits, we use the pattern r'(\d)\1+':

• (\d) − Captures a single digit in a group

• \1+ − Matches one or more occurrences of the same digit captured in group 1

This pattern finds consecutive repeating digits like "22", "333", or "4444".

Method 1: Find First Repeating Digit

Use re.search() to find the first occurrence of repeating digits ?

import re

def find_first_repeat(number):
    match = re.search(r'(\d)\1+', str(number))
    if match:
        return match.group()
    else:
        return "No repeats"

# Test the function
result = find_first_repeat(122345)
print("First repeating digits:", result)

First repeating digits: 22

Method 2: Find All Repeating Digits

Use re.findall() to get all repeating digit sequences ?

import re

def find_all_repeats(number):
    matches = re.findall(r'((\d)\2+)', str(number))
    if matches:
        return [group[0] for group in matches]
    else:
        return ["No repeats"]

# Test the function
result = find_all_repeats(122334455)
print("All repeating digits:", result)

All repeating digits: ['22', '33', '44', '55']

Method 3: Count Repeating Sequences

Count how many times each repeating pattern appears ?

import re

def count_repeats(number):
    matches = re.findall(r'((\d)\2+)', str(number))
    counts = {}
    for full_match, digit in matches:
        counts[full_match] = counts.get(full_match, 0) + 1
    return counts

# Test the function
result = count_repeats(12233445555)
print("Count of repeating digits:", result)

Count of repeating digits: {'22': 1, '33': 1, '44': 1, '5555': 1}

Method 4: Find Longest Repeating Sequence

Identify the longest sequence of consecutive repeating digits ?

import re

def longest_repeat(number):
    matches = re.findall(r'((\d)\2+)', str(number))
    if matches:
        return max([group[0] for group in matches], key=len)
    else:
        return "No repeats"

# Test the function
result = longest_repeat(122333444455555)
print("Longest repeating sequence:", result)

Longest repeating sequence: 55555

Comparison of Methods

Conclusion

Regular expressions provide an efficient way to find repeating digits in numbers. Use re.search() for the first match, re.findall() for all matches, and combine with additional logic for counting or finding the longest sequence based on your specific requirements.