pip "requires a different Python" - Version Constraint Failures

A package declares a Requires-Python range, and the interpreter pip is using falls outside it. pip skips that release - or every release - and the install fails.

What this error means

pip refuses a package or a specific version, noting it requires a different Python. Sometimes it silently picks a much older compatible version instead, which then breaks at runtime.

ERROR: Package 'cryptography' requires a different Python: 3.7.9 not in '>=3.8'
ERROR: Could not find a version that satisfies the requirement cryptography>=42 (from versions: ...)

Common causes

The interpreter is older than the package needs

Modern releases drop old Python versions. On Python 3.7 a package requiring >=3.8 is rejected, and pip may fall back to an ancient version of it.

The interpreter is newer than the package supports

Some packages cap their upper bound (<3.12). On a brand-new Python they have no compatible release and pip reports no matching distribution.

How to fix it

Set the Python version explicitly in CI

Pin the interpreter to one that sits inside every dependency’s supported range.

- uses: actions/setup-python@v5
  with:
    python-version: '3.11'

Confirm which interpreter pip is actually using

1. Run python --version and python -m pip --version in the same step.
2. If they disagree with what you expect, your PATH or venv is pointing at a different interpreter.
3. Invoke pip as python -m pip so it always matches the active interpreter.

How to prevent it

• Declare requires-python in your own project so consumers get a clear error.
• Test against the exact Python versions you support in a CI matrix.
• Avoid tracking the newest Python release before your dependencies support it.

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