I stumbled on this (--user flag) only the other day and it simplified things immensely. Too much information, various ways of doing things explained in bits and pieces over the decades makes it look confusing.
Often there is a very simple way, even in Python packaging and deploying. In my situation the easiest way began along these lines --
1. Install python3 for the local user from the source distribution (make sure you have compilers etc that the configure check lists out)
2. After compiling the sources and finishing with 'make install', make Python available in your local search path
3. And use pip with this magical --user flag as needed. No virtual env, conda, etc etc.
4. Leave HOMEPATH etc alone as this conflicts with the setup of the admin's system wide installs (when you su)
Doesn't that just install into a global-to-the-user path? Isn't one of the things we're trying to avoid is conflicts between these tools. For example, pip is now more freely breaking compatibility. I now need to ensure if my different packaging tools are compatible with my version of pip all installed in my user location.
Often there is a very simple way, even in Python packaging and deploying. In my situation the easiest way began along these lines --
1. Install python3 for the local user from the source distribution (make sure you have compilers etc that the configure check lists out)
2. After compiling the sources and finishing with 'make install', make Python available in your local search path
3. And use pip with this magical --user flag as needed. No virtual env, conda, etc etc.
4. Leave HOMEPATH etc alone as this conflicts with the setup of the admin's system wide installs (when you su)
Things can go smoothly with pip alone.