Interlude: Tools for debugging and visualization

As your RE gets complicated, it can get difficult to debug when you run into issues. Building your RE step by step from scratch and testing against input strings will go a long way in correcting the problem. To aid in such a process, you could use various online tools.

regex101

regex101 is a popular site to test your RE. You'll have to first choose the flavor as Python. Then you can add your RE, input strings, choose flags and an optional replacement string. Matching portions will be highlighted and explanation is offered in separate panes.

The below image is a screenshot from this link — regex101: r'ab{0,2}c'

Do explore all the features provided by the site. There's a quick reference and other features like link sharing, code generator, quiz, cheatsheet, etc.

debuggex

Another useful tool is debuggex which converts your RE to a railroad diagram, thus providing a visual aid to understanding the pattern.

The below image is a screenshot from this link — debuggex: r'\bpar(en|ro)?t\b'

re(gex)? playground

As already mentioned in the introduction chapter, I wrote an interactive TUI app for interactive practice. See PyRegexPlayground repo for installation instructions and usage guide.

re(gex)? exercises

I wrote another TUI app to help you solve exercises from this book interactively. See PyRegexExercises repo for installation steps and app_guide.md for instructions on using this app.

Here's a sample screenshot:

regexcrossword

For practice, regexcrossword is often recommended. It only supports JavaScript, so some of the puzzles may not work the same with Python syntax. See regexcrossword: howtoplay for help.

Summary

This chapter briefly presented tools that can help you with understanding and interactively solving/debugging regular expressions. Syntax and features can vary, sometimes significantly, between various tools and programming languages. So, ensure that the program you are using supports the flavor of regular expressions you are using.