Understanding Python re(gex)?

Learn Python Regular Expressions step-by-step from beginner to advanced levels with hundreds of examples and exercises. The standard library re and the third-party regex module are covered in this book. Visit https://youtu.be/2x2n7ynamm8 for a short video about the book.

The book also includes exercises to test your understanding, which are presented together as a single file in this repo — Exercises.md.

For solutions to the exercises, see Exercise_solutions.md.

You can also use this interactive TUI app to practice most of the exercises from the book.

See Version_changes.md to keep track of changes made to the book.

E-book

• You can purchase the pdf/epub versions of the book using these links:
  • https://leanpub.com/py_regex
  • https://learnbyexample.gumroad.com/l/py_regex
• You can also get the book as part of these bundles:
  • All books bundle bundle from https://leanpub.com/b/learnbyexample-all-books or https://learnbyexample.gumroad.com/l/all-books
  • Learn by example Python bundle from https://leanpub.com/b/python-bundle or https://learnbyexample.gumroad.com/l/python-bundle
  • Awesome Regex bundle from https://leanpub.com/b/regex or https://learnbyexample.gumroad.com/l/regex
• See https://learnbyexample.github.io/books/ for a list of other books

For a preview of the book, see sample chapters.

The book can also be viewed as a single markdown file in this repo. See my blogpost on generating pdf/epub from markdown using pandoc if you are interested in the ebook creation process.

For the web version of the book, visit https://learnbyexample.github.io/py_regular_expressions/

Testimonials

I love your books on regex...As a student from the Digital VLSI space, it is indeed useful now and definitely in the future. It's really well written and really easy to understand the examples.

— feedback on reddit

Feedback and Contributing

⚠️ ⚠️ Please DO NOT submit pull requests. Main reason being any modification requires changes in multiple places.

I would highly appreciate it if you'd let me know how you felt about this book. It could be anything from a simple thank you, pointing out a typo, mistakes in code snippets, which aspects of the book worked for you (or didn't!) and so on. Reader feedback is essential and especially so for self-published authors.

You can reach me via:

• Issue Manager: https://github.com/learnbyexample/py_regular_expressions/issues
• E-mail: echo 'bGVhcm5ieWV4YW1wbGUubmV0QGdtYWlsLmNvbQo=' | base64 --decode
• Twitter: https://twitter.com/learn_byexample

Table of Contents

1. Preface
2. Why is it needed?
3. re introduction
4. Anchors
5. Alternation and Grouping
6. Escaping metacharacters
7. Dot metacharacter and Quantifiers
8. Interlude: Tools for debugging and visualization
9. Working with matched portions
10. Character class
11. Groupings and backreferences
12. Interlude: Common tasks
13. Lookarounds
14. Flags
15. Unicode
16. regex module
17. Gotchas
18. Further Reading

Acknowledgements

• Python documentation — manuals and tutorials
• /r/learnpython/, /r/Python/ and /r/regex/ — helpful forums for beginners and experienced programmers alike
• stackoverflow — for getting answers to pertinent questions on Python and regular expressions
• tex.stackexchange — for help on pandoc and tex related questions
• canva — cover image
• Warning and Info icons by Amada44 under public domain
• oxipng, pngquant and svgcleaner — optimizing images
• David Cortesi for helpful feedback on both the technical content and grammar issues
• Kye and gmovchan for spotting a typo
• Hugh's email exchanges helped me significantly to improve the presentation of concepts and exercises
• Christopher Patti for reviewing the book, providing feedback and brightening the day with kind words
• Users 73tada, DrBobHope, nlomb and others for feedback in this reddit thread
• mdBook — for web version of the book
  • mdBook-pagetoc — for adding table of contents for each chapter
  • minify-html — for minifying html files

Special thanks to Al Sweigart. His Automate the Boring Stuff book was instrumental for me to get started with Python.

License

The book is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

The code snippets are licensed under MIT, see LICENSE file.