# Lesson Learned #001: Dependency Version Conflicts

## Issue Name
Dependency Version Conflicts in Requirements Files

## Date
2025-08-02

## Description
During project setup, encountered version conflicts with Python package dependencies:
- `pytest-dash==2.5.0` - Version did not exist in PyPI (max available: 2.1.2)
- `python-bcrypt==4.1.2` - Incorrect package name (should be `bcrypt==4.1.2`)

## Error Messages
```
ERROR: Could not find a version that satisfies the requirement pytest-dash==2.5.0 
(from versions: 0.1.0, 0.1.1, 0.1.2, 0.1.3, 0.2.0rc1, 0.2.0rc2, 0.2.0rc3, 1.0.0, 1.0.1, 1.1.0, 2.0.0rc1, 2.0.0rc2, 2.0.0rc3, 2.0.0rc4, 2.0.0rc5, 2.0.0, 2.1.0, 2.1.1, 2.1.2)

ERROR: Could not find a version that satisfies the requirement python-bcrypt==4.1.2 
(from versions: 0.3.1, 0.3.2)
```

## Root Cause
1. Incorrect package versions specified without checking PyPI availability
2. Wrong package name used for bcrypt library

## Solution Applied
1. **Updated pytest-dash version**:
   - Changed from `pytest-dash==2.5.0` to `pytest-dash==2.1.2`
   - Verified latest available version on PyPI

2. **Fixed bcrypt package name**:
   - Changed from `python-bcrypt==4.1.2` to `bcrypt==4.1.2`
   - Used correct package name

## Files Modified
- `requirements-backend.txt` - Fixed bcrypt package name
- `requirements-frontend.txt` - Updated pytest-dash version

## Prevention Strategy
1. Always verify package versions exist on PyPI before adding to requirements
2. Use `pip search` or check PyPI website for correct package names
3. Consider using version ranges instead of exact pins for non-critical dependencies
4. Implement CI/CD checks to validate requirements files

## Impact
- ✅ All dependencies now install successfully
- ✅ Project setup process is streamlined
- ✅ Development environment can be started without version conflicts