Regular Expressions in Python

Regular expressions (regex) are a powerful tool for working with strings in Python. They allow you to search for patterns, validate data, and extract specific information.

Basics of Regex

In Python, the re module provides a set of functions for working with regular expressions.

Matching a Pattern

The simplest regex pattern is to match an exact string. For example, the pattern r"hello" will match any occurrence of the string “hello” in the input.

import re

pattern = r"hello"
text = "hello world"
result = re.search(pattern, text)

if result:
    print("Pattern found!")

Common Regex Patterns

Here are some common patterns used in Python:

• \d: any digit (0-9)
• \w: any alphanumeric character
• \s: any whitespace character

Example:

pattern = r"\d{3}-\d{2}-\d{4}"
text = "My SSN is 123-45-6789."
result = re.search(pattern, text)

if result:
    print(f"SSN found: {result.group()}")

References and Grouping

You can also use references and grouping in regex. Groups are defined using parentheses, and references can be made using \1, \2, etc.

pattern = r"(\d{3})-(\d{2})-(\d{4})"
text = "SSN: 123-45-6789"
result = re.search(pattern, text)

if result:
    print(f"Area Code: {result.group(1)}")

Regex Structure

graph TD;
    A[Regex Start] --> B[Match Digit];
    B --> C[Match Dash];
    C --> D[Match More Digits];
    D --> E[Regex End];

Conclusion

Learning regular expressions can drastically improve your ability to handle and process strings in Python.