[Python-Dev] PEP 405 (pyvenv) and system Python upgrades

[Terry Reedy]

On 5/4/2012 11:58 PM, Glenn Linderman wrote:
> On 5/4/2012 8:48 PM, Terry Reedy wrote:
>> CPython is developed, tested, packaged, distributed, and installed as
>> one unit. It is intended to be run as one package. If something caches
>> a copy of python.exe, it seems to me that it should check and update
>> as needed. Could venv check the file date of the current python.exe
>> versus that of the one cached, much like is done with .pyc compiled
>> code caches?
>
> I almost wrote this response (using different words, but the same idea)
> but concluded that:
>
> 1) Python wouldn't run far without its standard library, so a venv check
> would have to be very early, and likely coded in C, and therefore
> probably has to be part of Python.exe
>
> 2) If it was not part of Python.exe, it would have to work similarly to
> the launcher, and there would be yet one more process sitting around
> waiting for Python to exit (on Windows, where there is no exec).
>
> So I concluded that probably Python.exe needs to make the check, but if
> it is aware it existing in venv, it might be able to put out a better
> message than "just" the mismatch between exe and lib; or at least the
> message should mention the possibility of an old venv cache.

The gist of my response is that the venv 'tail' should way the python 
'dog' as little as possbile.

I also wonder how often such incompatibility occurs. Optionally changing 
the de facto semantics of CPython's built-in dict in bug-fix releases 
was a rather unique event. I am sure we would all be happy to never have 
to do such again.

-- 
Terry Jan Reedy