Great question—this is a common point of confusion when working with older PyPI URL patterns! Let me break this down clearly:

Why the prefix link doesn’t open in browsers #

The URL prefix https://pypi.python.org/packages/source/p/ is part of PyPI’s legacy repository structure. While PyPI’s public frontend has been updated over the years to use a more user-friendly interface, this old path doesn’t map to any browsable page on the modern site. However, the underlying file storage for source packages still respects this pattern—so even though you can’t browse the directory in a browser, direct URLs to specific package tarballs (like your ${SRCNAME}-${PV}.tar.gz path) will still resolve to the actual file.

How developers originally learned these URL patterns #

These structured URLs weren’t some secret trick—they were well-documented and baked into early PyPI tooling:

• PyPI followed a strict, predictable naming convention for source packages from its early days:

  https://pypi.python.org/packages/source/<first letter of package>/<package name>/<package name>-<version>.tar.gz
  

  This convention was outlined in PyPI’s official documentation and referenced in tools like setuptools and older versions of pip.
• Early versions of pip and package automation tools automatically constructed these URLs when fetching source distributions (for example, when using pip install --no-binary :all:). Developers would observe this behavior in logs or tool source code to replicate the pattern in custom scripts.
• Many legacy scripts (like the one you’re using) were written during this era, passing down the URL structure through maintenance and reuse.

A note on modern PyPI practices #

If you’re looking to update your script for reliability, consider switching to PyPI’s current standard:

• Use the files.pythonhosted.org domain for direct package downloads (this is the modern backend storage, and direct file URLs here will work in browsers too).
• For more flexibility, fetch package metadata via PyPI’s JSON API (e.g., https://pypi.org/pypi/${SRCNAME}/${PV}/json), which includes all valid download URLs for the package version—this avoids hardcoding URL patterns entirely.

内容的提问来源于stack exchange，提问作者Chandra Sekhar