# ERROR: Cannot install numpy==1.26.4 and Cython>=3.0 because these package versions have conflicting dependencies.
The conflict is caused by:
    The user requested numpy==1.26.4
    Cython 3.0.10 depends on numpy>=2.0

- **ID:** `python/pip-build-deps-conflict-cython-numpy`
- **Domain:** python
- **Category:** install_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Build-time dependencies and runtime pins were mixed in the same requirements file, creating an unsatisfiable graph.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **** (92% success)
   ```
   [build-system]
requires = ["setuptools>=68", "wheel", "Cython>=3.0", "numpy>=2.0"]
build-backend = "setuptools.build_meta"
# then
pip install .
   ```
2. **** (85% success)
   ```
   echo 'numpy==1.26.4' > constraints.txt
pip install -c constraints.txt Cython>=3.0
   ```

## Dead Ends

- **** — Skips dependency installation entirely, leaving the environment broken at runtime. (80% fail)
- **** — Legacy resolver may install an inconsistent set silently, causing runtime errors. (70% fail)
- **** — May pull numpy 2.x, incompatible with other pinned packages in the project. (50% fail)