This often happens in corporate environments where firewalls or proxies intercept traffic using self-signed certificates that pip does not trust.
Corporate firewalls, VPNs, or restricted local network settings can block the specific ports or domains required by PyPI.
Older versions of pip may attempt to use deprecated URLs like http://pypi.python.org/simple/ , which are no longer supported for secure downloads. download error on https //pypi.org/simple/cython/
For Linux users, installing through the system repository can avoid PyPI network issues entirely. Stack Overflowhttps://stackoverflow.com
The first step is always ensuring your package manager is current. Modern pip versions have better handling for HTTPS and modern security protocols. python -m pip install --upgrade pip Use code with caution. 2. Bypass SSL Verification (Use with Caution) This often happens in corporate environments where firewalls
On some systems, especially macOS or manual Python builds, the ssl module might be missing or misconfigured, leading to "Max retries exceeded" errors. Troubleshooting and Fixes
If you are behind a corporate firewall and getting SSL: CERTIFICATE_VERIFY_FAILED , you can temporarily mark PyPI as a "trusted host" to bypass verification. For Linux users, installing through the system repository
If pip is trying to reach an old or incorrect URL, you can force it to use the correct simple index. pip install cython --index-url https://pypi.org/simple/ Use code with caution. 4. Use System Package Managers
Several factors can prevent pip from reaching the Cython index: