- The true power of regular expressions — it also includes a nice explanation of what regular means in this context
- softwareengineering: Is it a must for every programmer to learn regular expressions?
- softwareengineering: When you should NOT use Regular Expressions?
- codinghorror: Now You Have Two Problems
- wikipedia: Regular expression — this article includes discussion on regular expressions as a formal language as well as details on various implementations
- swtch - stuff about regular expression implementation engines
Note that some of these resources are not specific to Python, so use them with caution and check if they apply to Python's syntax and features.
- docs.python: Regular Expression HOWTO
- stackoverflow: python regex
- PythonVerbalExpressions — construct regular expressions with natural language terms
- CommonRegex — collection of common regular expressions
- Awesome Regex — curated collection of libraries, tools, frameworks and software
- Generate strings that match a given regular expression
- stackoverflow: regex FAQ
- stackoverflow: regex tag is a good source of exercise questions
- rexegg — tutorials, tricks and more
- regular-expressions — tutorials and tools
- regexcrossword — tutorials and puzzles, only supports JavaScript flavor
- regex101 — visual aid and online testing tool for regular expressions, select flavor as Python before use
- debuggex — railroad diagrams for regular expressions, select flavor as Python before use
- rexegg: best regex trick
- regular-expressions: matching numeric ranges
- regular-expressions: Continuing at The End of The Previous Match
- regular-expressions: Zero-Length Matches
- stackoverflow: Greedy vs Reluctant vs Possessive Quantifiers
- cloudflare: Details of the Cloudflare outage on July 2, 2019 — see appendix for details about CPU exhaustion caused due to regular expression backtracking