A full mirror of PyPI, took 1 day ago, is currently available on the Debsources machine under /srv/pypi . Ask @zack if you don't have access and would like to have a look at its structure.

> PyPI is easy to mirror [1], and a network of public mirrors [2] already exist. The Python package bandersnatch [3] automate the task of setting up an initial mirror and keeping it up to date.

Most doc links from this sentence are either broken ([1] is 404) or not accessible ([2] is 403) except for the bandersnatch tool [3].
Looking at the faq [4], they also (now?) recommend bandersnatch. Quoting it:

How can I run a mirror of PyPI?

    If you need to run your own mirror of PyPI, the bandersnatch [3] project is the recommended solution. 
    Note that the storage requirements for a PyPI mirror would exceed 1 terabyte—and growing!

[1] https://pypi.python.org/mirrors
[2] https://www.pypi-mirrors.org/
[3] https://pypi.org/project/bandersnatch/ (that url seems stable ;)
[4] https://pypi.org/help/#mirroring

In T420#21471, @ardumont wrote:

Looking at the faq [4], they also (now?) recommend bandersnatch. Quoting it:

not sure if that's useful to you, but just in case: the out-of-dated-ness is most likely due to the fact that, since I opened this task 2 years ago, pypi has been completely revamped. See, e.g.:

• https://blog.python.org/2018/04/new-pypi-launched-legacy-pypi-shutting.html
• https://lwn.net/Articles/752192/

better LWN link to the actual article covering this: https://lwn.net/Articles/751458/

the out-of-dated-ness is most likely due to the fact that, since I opened this task 2 years ago...

yes, i guessed as much.

pypi has been completely revamped. See, e.g.:...

And thanks for the links ;)