[Python-ideas] install pip packages from Python prompt

[Paul Moore]

On 30 October 2017 at 15:53, Antoine Pitrou <solipsis at pitrou.net> wrote:
> On Tue, 31 Oct 2017 01:44:10 +1000
> Nick Coghlan <ncoghlan at gmail.com> wrote:
>>
>> A few specific notes here:
>>
>> 1. As you say, this sort of already works in notebooks, since instructors
>> can say to run "!pip install requests" and then restart the language kernel.
>> 2. We could probably replicate that style in IDLE, since that runs user
>> code in a subprocess, similar to the way Jupyter language kernels are
>> separate from the frontend client
>> 3. We can't replicate it as readily in the regular REPL, since that runs
>> Python code directly in the current process, but even there I believe we
>> could potentially trigger a full process restart via execve (or the C++
>> style _execve on Windows)
>>
>> (We'd want a real process restart, rather than emulating it by calling
>> Py_Initialize & Py_Finalize multiple times, as not every module properly
>> supports multiple initialise/finalise cycles within a single process, and
>> module-specific quirks are exactly what we'd be trying to avoid by forcing
>> an interpreter restart)
>
> The main difference, though, is that a notebook will reload and
> replay all your session, while restarting the regular REPL will simply
> lose all current work.  I think that makes the idea much less
> appealing.

Also, on Windows, I believe that any emulation of execve either leaves
the original process in memory, or has problems getting console
inheritance right. It's been a long time since I worked at that level,
and things may be better now, but getting a robust "restart this
process" interface in Windows would need some care (that's one of the
reasons the py launcher runs Python as a subprocess rather than doing
any sort of exec equivalent).

Paul