👀 Views: 5 💬 Answers: 1 📅 Created: 2025-06-08

regex python validation Python

Could someone explain I'm refactoring my project and I'm maintaining legacy code that Quick question that's been bugging me - I'm trying to validate a string format where the input can be a series of alphanumeric characters, optionally separated by hyphens. The pattern should allow for one or more alphanumeric segments, like `abc-123`, `xyz-456-789`, or just `hello`. However, I'm struggling with edge cases that include leading or trailing hyphens, as well as multiple consecutive hyphens. Here's the regex I've been using: ```python import re pattern = r'^[a-zA-Z0-9]+(-[a-zA-Z0-9]+)*$' ``` This seems to work for most inputs, but when I test strings like `-abc`, `abc-`, or `abc--123`, it incorrectly returns true instead of false. I would expect these cases to be invalid. I've tried modifying the regex to: ```python pattern = r'^(?!-)(?!.*--)[a-zA-Z0-9]+(-[a-zA-Z0-9]+)*(?<!-)$' ``` This approach uses negative lookaheads and lookbehinds to prevent leading, trailing, and consecutive hyphens. However, I'm still getting unexpected behavior. For instance, the string `abc--123` returns true, which should not happen. I've also looked into using the `fullmatch` method but it doesn't seem to change the results in this case. I'm using Python 3.9 and the standard `re` library. Can someone guide to tweak this regex to correctly exclude those edge cases while still validating the desired formats? My development environment is macOS. Has anyone else encountered this? For reference, this is a production application. Thanks for any help you can provide! I'm developing on Windows 10 with Python. Any help would be greatly appreciated!