Debugging bcrypt compatibility issue with passlib in Python

Day 96 of Backend/Cloud/DevOps Journey - Debugging bcrypt Compatibility Issues Today was all about real-world debugging. Spent the session troubleshooting a passlib/bcrypt compatibility issue that persisted even after switching Python versions. What I accomplished: • Installed Python 3.12 via Homebrew to replace Python 3.14 (learned that compilation from source takes time due to C extension building) • Discovered the issue wasn't Python version but bcrypt library version incompatibility with passlib • Pinned bcrypt to version 4.0.1 to resolve passlib's internal self-test failures • Successfully tested all auth utilities: hash_password, verify_password, create_access_token, verify_token • Learned why pinning dependency versions in requirements.txt prevents environment inconsistencies across deployments • Updated verify_token() to include algorithms parameter for security best practices Technical insights: • Homebrew's "make" step compiles C source code to machine code which is CPU-intensive and time-consuming • Virtual environments are tied to the Python version that created them—you cannot switch versions without recreating the venv • The bcrypt 72-byte password limit caused passlib's detect_wrap_bug() self-test to fail on newer bcrypt versions (4.1+) • Pinning dependencies (bcrypt==4.0.1) ensures consistent behavior across development, staging, and production environments • The algorithms parameter in jwt.decode() prevents algorithm confusion attacks—always specify explicitly • Real-world debugging often means the obvious fix (switching Python versions) doesn't work and requires deeper investigation • Library compatibility issues are common in production—this is why teams use stable Python versions not bleeding edge Key lesson: When an error persists after the "obvious" fix, dig deeper into the dependency chain. The root cause was bcrypt library version, not Python version. Auth system now fully functional: password hashing with bcrypt salting, password verification, JWT creation with expiration, and token decoding with validation. Next steps: Complete User model in SQLAlchemy, create users table, build registration and login endpoints. #100DaysOfCode #Python #FastAPI #Debugging #bcrypt #DependencyManagement #BackendDevelopment #CloudEngineering #DevOps #LearningInPublic #TechCareer #BuildInPublic

To view or add a comment, sign in

Explore content categories