Python Regex Cheat Sheet With Examples

Regular expressions, or regex, are powerful tools for string manipulation and pattern matching in Python. This Python regex cheat sheet provides essential regex patterns, regex examples, and tips for mastering regex syntax. Whether you're a beginner or an advanced user, this cheat sheet is your go-to regex reference for efficient text processing.

What is Regex?

Regex, short for regular expressions, is a sequence of characters defining a search pattern. It is commonly used for tasks such as regex validation, regex substitution, regex search, and regex extraction.

Basic Regex Syntax

Understanding regex basics is crucial for crafting effective patterns. Below is a table highlighting fundamental regex syntax:

Regex Quantifiers

Regex quantifiers define how many times a character or group should occur:

• * - Matches 0 or more times
• + - Matches 1 or more times
• ? - Matches 0 or 1 time
• {n} - Matches exactly n times
• {n,m} - Matches between n and m times

Regex Groups and Backreferences

Using regex groups helps capture specific parts of a match. Regex backreferences allow you to reuse these groups in patterns:

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import re
pattern = r"(abc)\1"
match = re.match(pattern, "abcabc")
print(match.group(0))  # Output: abcabc

Advanced Regex Features

1. Lookaround Assertions

Regex lookaround helps match patterns without consuming characters:

• (?=...) - Positive lookahead
• (?!...) - Negative lookahead
• (?<=...) - Positive lookbehind
• (?<!...) - Negative lookbehind

2. Regex Substitution

Replace matched patterns with regex substitution:

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text = "hello world"
pattern = r"\bworld\b"
result = re.sub(pattern, "Python", text)
print(result)  # Output: hello Python

Practical Regex Examples

Below are some regex examples demonstrating common use cases:

• Email Validation: [a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+
• Extracting Dates: \d{4}-\d{2}-\d{2}
• Finding URLs: https?://[^\s]+

FAQs

1. What is a Python regex cheat sheet?

A Python regex cheat sheet is a quick reference guide containing common regex patterns, regex syntax, and regex examples to simplify regular expression usage.

2. How can I test my regex patterns?

You can use online tools like regex tester, regex101, or regexr to experiment with and debug regex patterns.

3. What are regex quantifiers?

Regex quantifiers define the number of times a character, group, or set should appear in a match.

4. Where can I find a printable regex cheat sheet?

A regex cheat sheet printable can be downloaded from platforms like GitHub or regex101 as a regex cheat sheet pdf.

5. What are regex backreferences used for?

Regex backreferences allow reusing previously captured groups within a pattern, enabling advanced pattern matching.

Conclusion

This Python regex cheat sheet with examples provides a comprehensive overview of regex patterns, regex syntax, and advanced features. With practice, you can master regex tricks and streamline tasks like regex validation, regex extraction, and regex substitution.