On 13Sep2016 1500, Paul Moore wrote:
On 13 September 2016 at 21:12, Thomas Kluyver <tho...@kluyver.me.uk> wrote:
One thing I'd quite like to see Python grow is a standard function to
install packages from inside Python.
That's not too hard in principle - pip.main(['install', package]) is
basically all you'd need (modulo various design details, and wrapping
it in a nice user friendly function). The bigger problems are:
1. pip is an independent module (albeit shipped with Python) and it's
not clear to what extent Python would want a builtin function that
depends on a non-stdlib module. But that's not a technical issue.
2. Python's module system isn't really designed around installing new
modules while a process is running. There's caching involved, so the
effects can be unpredictable. It's difficult to know whether the
benefits (avoiding confused users who tried to install from a Python
prompt) would outweigh the costs (confused users having installed a
module but not being able to see it because the module system didn't
notice things had changed).
I'm not honestly sure how big the "installing while a process is
running" issue would be - I did a few simple experiments and couldn't
immediately trigger weirdness, but I believe it can happen. And things
get significantly worse if we allow upgrades from the Python prompt
rather than just installs (e.g., if you have already imported
something from the old version and then upgrade).
Overall, it'd probably be a nice thing to have, but it's nowhere near
as simple as it seems at first glance.
Paul
I think it's one of these things where we should suck it up and let the
90% case work fine, then display a big fat warning if anything weird may
have happened and let users sort it out themselves.
A simple builtin that tries to run "sys.executable -m pip {args}" in a
subprocess and displays "success", "success but you should probably
restart Python now", "failed because you don't have pip", "failed and
have all the output" is going to make lots of people happy, even if it
upsets those who want it to be perfect in every scenario.
Cheers,
Steve
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