[Eric] install.py does not seem to respect virtual environments

[Detlev Offenbach]

Hello Ross,

thank you very much for your lengthy explanation. And the baseline summary of 
all written words is:

Don't use the py launcher. Be explicit when invoking the install.py script.

Regards,
Detlev

Am Samstag, 7. Dezember 2019, 22:05:34 CET schrieb Boylan, Ross:
> Having stepped through the code and examined the documents, it seems to me
> the documentation has some unresolved contradictions about what rules apply
> in this case, but that either set that could apply mean py install.py
> should invoke the venv's Python 3.7. Which is not what happens. This seems
> like more of a Python issue than an eric issue, though it's possible eric
> could work around it by, e.g., changing the #! line at the start of
> install.py.*
> 
> Context: invoking "py installer.py" from within a 3.7 virtual environment on
> Win10.  The first line of installer.py is #!/usr/bin/env python3
> 
> sys.exec_prefix (e.g., line 184 of initGlobals()) points at my user-specific
> 3.8 installation.  base_exec_prefix and executable do as well. The
> documentation for sys says that exec_prefix should point to a virtual
> environment if it is invoked in that context, so this seems like an error.
> 
> However, the documentation for the py launcher in the Windows section of
> "Python Setup and Useage" says 2 things: Section 3.7.1.2 says if py is
> invoked from a virtual environment with no explicit version specified, it
> will run the virtual environment's interpreter. The behavior is
> inconsistent with that.
> 
> But Section 3.7.2 discusses scripts and #! lines and it is not clear if one
> invokes a script from a virtual environment whether 3.7.1.2 or 3.7.2 is
> supposed to apply.  Supposing the latter, the relevant part says that if
> the /usr/bin/env form is used the executable PATH will be searched. 
> However, because I am in an active virtual environment, the first entry in
> my PATH points to the venv's Scripts directory, which again should get me
> the venv Python 3.7, not the non-virtual 3.8.
> 
> So whether 3.7.1.2 or 3.7.2 governs, the documents seem to say I should get
> my venv python interpreter, but I don't.  Or at least, sys.exec_prefix and
> friends aren't set consistent with that.
> 
> There are a couple of wrinkles.  If py doesn't inherit the PATH from my
> terminal session, getting my default PATH instead, it will get a PATH that
> only has Python 3.8 on it (because of the options I selected on
> installation of Python 3.7 and 3.8).  So that could result in getting the
> "wrong" python.  Also, I recall seeing some caution/bug that user settings
> in PATH were processed after system settings.  Even if true, I'm not sure
> how it's relevant, but if my venv path is processed after the python 3.8
> path the /usr/bin/env interpretation by py would pick 3.8.
> 
> *I replaced the #! line with a blank line and got the venv python for
> sys.exec_prefix.  So I think that's enough to fix this problem, though
> admittedly it might cause other problems :(

-- 
Detlev Offenbach
detlev at die-offenbachs.de