pip 'ERROR: Could not find a version that satisfies the requirement X' / 'ERROR: No matching distribution found for X': what are the real causes and fixes?

Cause: pip looked at the index (PyPI or your configured one) and found no release of that name that it is allowed to install on this machine. Common reasons, roughly by frequency: a typo in the package name; the package's releases declare a Requires-Python that excludes your interpreter (pip filters those out, so a too-old or too-new Python leaves nothing); no wheel exists for your platform or architecture and a source build is not allowed (--only-binary) or fails; the requested version does not exist or is only a pre-release (pip ignores pre-releases unless --pre or an explicit pre-release version); the index URL, proxy or custom index is wrong or unreachable; or the pip is old and does not handle modern metadata. Fix (best first): 1. Check the name and version: pip index versions <name> (or look the project up on the index) and compare with what you typed. Check python --version and pip --version, and use python -m pip so pip and python match. 2. Look at the package's Python-version support. If your Python is outside it, use a supported interpreter (create a venv with the right Python) or choose a release that supports yours: pip install "name==<version that supports your Python>". For another target Python, pip install has --python-version for checks, used together with the platform and --only-binary options. 3. Run pip install -v <name> to see which files were considered and why each was rejected (Requires-Python, wrong platform tag). 4. Upgrade pip inside the venv: python -m pip install --upgrade pip, so it understands current wheel tags and metadata. 5. Check the index and network: pip config list for index-url and extra-index-url, proxy settings, and whether the private index mirrors this package. Use only indexes you trust; adding extra indexes can open dependency-confusion risk. 6. Avoid --ignore-requires-python as a fix; it installs code on an interpreter the maintainers say it does not support. Verify: pip install <name> completes, and python -c "import <module>" works inside the same environment. Sources: https://pip.pypa.io/en/stable/cli/pip_install/ https://packaging.python.org/en/latest/guides/dropping-older-python-versions/