在 Windows 上彻底重新安装 Python 的最佳方法是什么？

Question

I tried to update Python 3.8.5. to 3.8.10 on a Windows 7 machine, but some part of Python's and/or pip 's messy installer/path/package management system bricked everything. Nobody I asked knows a canonical solution to this + pretty much everybody is suggesting a complete reinstallation.

Which is why I've now completely removed Python and have to reinstall Python, pip , and all my packages one by one. I've already uninstalled/removed Python and pip and downloaded the official Python 3.8.10 64-bit Windows installer as well as get-pip.py .

But despite spending days and days of reading, I can't see through Python's complicated mess of "user-specific vs. local vs. system-wide" installation schemes, varying package installations paths, the seemingly arbitrary variations introduced by using python vs. python -m , pip install vs. pip install --user etc. during package installations, and the regular whining about some PATH environment variables not being set properly etc. pp. - if you've ever used Python professionally, you'll have an idea of what I'm describing here.

Anyway - what I want to do now is make one clean installation where I stick to one set of rules for everything. All packages installed to one single superdirectory (vs. getting scattered all over the system) and all PATH variables set accordingly to the most universal and complete configuration possible (I don't want to see any complaints from Python ever again in this regard). Note that I'm the administrator of the machine, but working from a normal user account with Windows UAC enabled and want an installation for all users - the most general solution possible, no limiting scenarios that may cause the very problems I'm trying to avoid.

Also, I do not want to use virtual environments for now, but this is different topic I'm already working on independently. So no suggestions regarding venv .

Question: How to procede with the installation?

Possible sub-issues that need to be addressed:

1. Correct privileges for the Windows installer, eg the confusing "for all users (requires elevation)" and subsequent (second!) "Install for all users" options. The latter changes the installation path from C:\Users\<Username>\AppData\Local\Programs\Python\Python38 to C:\Program Files\Python38 and Windows UAC may prevent access of Python and/or pip to C:\Program Files\ without proper exception handling (eg user prompt) in place:

2. Usage of get-pip.py vs. some other methods to install pip , which also concerns the usage of python vs. python -m vs. pip install vs. pip install --user etc. in this context and subsequent installation of user packages.

3. Prevention of scattering/fragmentation of the Python development framework over the system/different folders/different users, causing eg annoying PATH or dependency issues/conflicts.

4. Defining the correct set of Windows path variables under these requirements and addressing concerns/doubts about Python's and pip 's ability of reliably handling this issue on their own.

Note: I'm the owner/only user on this machine and therefore have administrator rights. Managing installations/environments for multiple users is not the subject here and of no interest for me.

Answer 1

Anyway - what I want to do now is make one clean installation where I stick to one set of rules for everything. All packages installed to one single superdirectory (vs. getting scattered all over the system) and all PATH variables set accordingly to the most universal and complete configuration possible (I don't want to see any complaints from Python ever again in this regard).

This is contradictory. A single installation with a common set of rules, every possible installed package, comprehensive PATH etc. is inherently not "clean" . The point of maintaining separate installations is so that one user's changes do not unexpectedly impact on the operation of another user's code . It is not possible to do this with a single installation. If you upgrade a library, for example, it affects every user who wrote code that uses that library, who must now check for incompatibilities.

Correct privileges for the Windows installer, eg the confusing "for all users (requires elevation)" and subsequent (second!) "Install for all users" options.

The first one means "Install the launcher for all users", which is why that checkbox is on the same line as "py launcher". (If you are not familiar with the Python launcher for Windows , please read the documentation .) it says "(requires elevation)" because the installer requires elevation in order to install this feature for all users. You do not need to do this if you have installed it from a previous version of Python.

and subsequent (second!) "Install for all users" options.

This is the option to install this version of Python for all users. The install directory changes according to the "for all users" setting, in the expected way.

Windows UAC may prevent access of Python and/or pip to C:\Program Files\ without proper exception handling (eg user prompt) in place

It will prevent write access without elevation, yes. This is by design, and it is why the option exists for per-user installations.

pip requires write access, because its purpose is to install libraries. I do not know whether it can request elevation from the command prompt; probably not. You can work around this by using the command in an elevated command window. With UAC enabled, you will not be able to install libraries into a Python for-all-users installation (ie, in Program Files): it is the explicit purpose of UAC to prevent that sort of thing.

Python normally does not require write access to these directories. The standard library does not need write access once the library is installed. There might be a problem if you uncheck "Precompile standard libraries"; I have not tested this and have stopped using Windows. Third-party libraries normally will not require write access for their own installation directories, either. If you encounter a problem, consult the documentation for that library.

Usage of get-pip.py vs. some other methods to install pip, which also concerns the usage of python vs. python -m vs. pip install vs. pip install --user etc. in this context and subsequent installation of user packages.

get-pip etc. are deprecated. They are tools intended to account for the fact that Python didn't always come bundled with pip . It does now. pip works the same way regardless of whether it was bundled with Python or installed to an older Python version separately. There is not a clear question here; there are several specific things that need to be researched and understood about how to use pip.