Explain what regular expressions are and what they are used for.

Regular expressions are patterns used for searching and manipulating text. They allow you to find, verify, and replace strings that match a certain format. In Python, the re module is used for working with regular expressions.

Example: checking if a string contains only digits:

import re
pattern = r'^\d+$'
text = '12345'
if re.match(pattern, text):
    print('The string contains only digits')
else:
    print('The string contains other characters')

Regular expressions are useful for data validation, log parsing, and search-and-replace operations in text.