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

Carl Meyer carl at oddbird.net
Mon May 7 00:07:32 CEST 2012

On 05/05/2012 04:40 AM, Antoine Pitrou wrote:

On Fri, 04 May 2012 14:49:03 -0600 Carl Meyer<carl at oddbird.net> wrote:

3) Symlink the interpreter rather than copying. I include this here for the sake of completeness, but it's already been rejected due to significant problems on older Windows' and OS X. Perhaps symlinking could be used at least on symlinks-friendly OSes? I expect older Windows to disappear one day :-) So the only left outlier would be OS X.

It certainly could - at one point the reference implementation did exactly this. I understand though that even on newer Windows' there are administrator-privilege issues with symlinks, and I don't know that there's any prospect of the OS X stub executable going away, so I think if we did this we should assume that we're accepting a more-or-less permanent cross-platform difference in the default behavior of venvs. Maybe that's ok; it would mean that for Linux users there'd be no need to run any venv-upgrade script at all when Python is updated, which is certainly a plus.

At one point it was argued that we shouldn't symlink by default because users expect venvs to be isolated and not upgraded implicitly. I think this discussion reveals that that's a false argument, since the stdlib will be upgraded implicitly regardless, and that's just as likely to break something as an interpreter update (and more likely than upgrading them in sync). IOW, if you want real full isolation from a system Python, you build your own Python, you don't use pyvenv.

Carl

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