'Python: Should I save PyPi packages offline as a backup?

My Python projects heavily depends on PyPi packages.
I want to make sure that: in any time in the future: the packages required by my apps will always be available online on PyPi.
For example:-
I found a project on Github that requires PyQt4.
when I tried to run it on my Linux machine,
it crashed on startup because it can't find PyQt4 package on PyPi.

NB: I know that PyQt4 is deprecated

I searched a lot to find an archive for PyPi that still holds PyQt4 package, but I couldn't find them anywhere.

so I had to rewrite that app to make it work on PyQt5.
I only changed the code related to the UI (ie: PyQt4).
other functions were still working.

so the only problem with that app was that PyQt4 package was removed from PyPi.



so, my question is: should I save a backup of the PyPi packages I use ?


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