[Distutils] Module Installation Issues

[Nick Coghlan]

On 14 September 2016 at 08:55, Donald Stufft <donald at stufft.io> wrote:
> Another problem, particularly on Windows, is going to be stuff like:
>
>>>> import someclibrary
>>>> pip.install(“thing”)  # Implicitly upgrades someclibrary
>
> In this case, this would explode because Python will have the someclibrary.dll locked and the upgrade will attempt to remove it.
>
> My fears here are that people are going to get really confused when they make state modifications to their Python environment and they don’t see those modifications reflected (because of sys.modules caching or what have you). You can possibly get around that with reload(), but we already know the problems that reload() has. Of course, that doesn’t stop Python from offering reload(), but I think the difference is that reload() is targeted towards people with weird edge cases who can understand the caveats while the hypothetical ``pip.install()`` is targeted towards people who are beginners who are still having problems figuring out the difference between the REPL and their shell, much less the vagaries of Python’s global state and attempting to modify that in a now running Python program.

While I'm normally not a fan, I think this is a case where a widely
ignored warning is the most sensible option - if people see *any* kind
of weirdness after doing a live package install, their first reaction
should be to restart their Python environment and see if the problem
goes away. In a lot of cases things will work fine (since a lot of
modules are well-behaved in this regard), and for those that aren't, a
restart is usually a sufficient remedial step.

To further reduce the support footprint, we can explicitly limit this
API to supporting installation using the *default* configuration
settings only - absolutely no configurability whatsoever other than an
optional version constraint on the package being installed.

Since this is a new API, we could also make it only do --user installs
when outside a virtual environment.

That said, to fend off requests for increased complexity in the
beginner focused `pip.install()` API, it may be necessary to finally
define a semi-supported `pip._custom_install()` API that exposes more
of the bells and whistles supported by `pip install`. The underscore
prefix would clearly indicate the officially unstable nature of the
API, and beginners are unlikely to reach for "pip._custom_install()"
when "pip.install()" exists.

> Perhaps a better idea would be to add some smarts to the REPL (but not to Python itself) that would detect something like:
>
>>>> pip install
>
> And print a better error message that gives a better indication about what’s gone wrong besides a SyntaxError?

I filed http://bugs.python.org/issue28140 for that - we should be able
to hook into the same system that gives special error messages for
"print message" and "exec code" in Python 3. (The related special
casing is actually in the SyntaxError constructor, so this would
affect non-interactive code as well, but I think that's fine for this
case).

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia