BUG: Installing on windows fails. --prefer-binary option for the venv pip is not recognized.

[JVanloofsvelt]

On Windows, the virtual environment created by installer.py comes with an old pip version. It complains about the option '--prefer-binary' since this option was not supported by the old pip version.

It might be related to the fact that I have an older Python 3.5 installation that came with an older pip version.

[JVanloofsvelt]

I did some research, apparently the installer has three strategies for creating a virtualenv:

1. using the builtin venv module
2. using virtualenv from site-packages if venv was not an option
3. Downloading virtualenv if virtualenv was not found

Remarks:

• The built-in 'venv' module uses the builtin 'ensurepip' module, which comes bundled with a pip version. This version cannot be updated, it is supposed to be frozen with the specific Python distribution/version.
• The '--prefer-binary' option for pip was added in pip version 18.0

How should the installer.py be modified then? IMO: use_venv() should fail (or rather be skipped) if the pip version that comes with ensurepip() is older than version 18.0.

[JVanloofsvelt]

I'm guessing I created this issue in the wrong repository. I created a copy in the Lektor repository: https://github.com/lektor/lektor/issues/808

[andoresuperesu]

Not the wrong repo if the fix can be applied to the installer script located here.

[JVanloofsvelt]

Thanks Andres, I was looking for it!

[CAM-Gerlach]

This can be closed along with #307 , presumably, since it sounds like the old installer script will be deprecated/removed if it isn't already.