Python Regular Expressions

Regular expressions (regex) are powerful tools for searching and manipulating text in Python. They allow you to define patterns for matching strings, which simplifies tasks like validating inputs, searching for specific data, or replacing content within strings.

Key Concepts

• What is a Regular Expression?
  • A regular expression is a sequence of characters that forms a search pattern.
  • It can be used for string searching, matching, and manipulation.
• The re Module
  • Python provides the re module for working with regular expressions.
  • You need to import this module to use regex functions.

Common Functions

1. re.match()
   • Checks for a match only at the beginning of the string.
   • Example:
2. re.search()
   • Searches the entire string for a match.
   • Example:
3. re.findall()
   • Returns a list of all matches in the string.
   • Example:
4. re.sub()
   • Replaces occurrences of a pattern with a specified string.
   • Example:

result = re.sub(r'\d+', 'number', 'abc123def456')
print(result)  # Output: abcnumberdefnumber

result = re.findall(r'\d+', 'abc123def456')
print(result)  # Output: ['123', '456']

result = re.search(r'\d+', 'abc123def')
print(result.group())  # Output: 123

import re
result = re.match(r'\d+', '123abc')
print(result.group())  # Output: 123

Special Characters

• . - Matches any character except a newline.
• ^ - Matches the start of a string.
• $ - Matches the end of a string.
• * - Matches 0 or more repetitions of the preceding element.
• + - Matches 1 or more repetitions of the preceding element.
• ? - Matches 0 or 1 repetition of the preceding element.
• [] - Matches any single character within the brackets.
• | - Acts as a logical OR.

Conclusion

Regular expressions are a powerful way to work with text in Python. By understanding the basic functions and special characters, you can effectively search, match, and manipulate strings with ease. This is particularly useful for tasks like data validation and text processing.