[IPython-dev] Discovering kernels/profiles

[MinRK]

I think that in general, we want to be able to specify the kernel on a
per-notebook basis, so we definitely need to remove the current 1:1
relationship of profile to kernel. Some ipython-wide location where kernel
providers can say "here I am" makes sense.


On Sat, Nov 9, 2013 at 1:49 PM, Thomas Kluyver <takowl at gmail.com> wrote:

> I'm starting to think about how newly installed kernels can be discovered
> by IPython, and the links between kernels and profiles.
>
> At the moment, the way to use a non-default kernel (such as IJulia) is to
> specify its arguments in a config value. As a shortcut, you can create a
> profile with this setting, and then launch IPython using that profile (e.g.
> --profile=julia). However, we'd like to make it possible to start different
> kernels from one notebook server (and presumably from one Qt console). When
> a kernel is installed, there should be a simple way for it to tell IPython
> of its existence, and how to start it.
>
> A profile is a collection of settings, along with its own command history.
> There may well be more than one profile for a given kernel - e.g. we ship a
> few Python profiles that load different libraries on startup. In some
> cases, it may also make sense to have more than one kernel per profile: the
> default profile is currently used for both Python 3 and Python 2. In most
> cases, however, it probably makes sense for each profile to be associated
> with one kernel.
>
> So, I propose:
> - On installation, kernels should place a small json file in a specific
> directory. There will be a per-user directory (e.g. ~/.ipython/kernels) and
> a systemwide one (e.g. /usr/share/ipython/kernels)
> - IPython will offer a mechanism to open a notebook (or run kernels by
> other means) with a specific profile
> - The list of 'profiles' will include the names of kernels that don't yet
> have a matching profile. When one of these is selected, a matching profile
> will be created - so the first time you use the Haskell kernel, say, a
> profile_haskell profile folder is made.
> - The profiles can specify a kernel definition file, instead of including
> kernel details directly in config. This allows the kernel definition to be
> updated later, if e.g. command line arguments change.
>
> Does this sound sensible?
>
> Then there's the question of how to handle multiple kernels sharing a
> profile. We could allow a general mechanism for this, or special case the
> Python 2/3 kernels, or just drop the possibility and force the Python
> kernels to use separate profiles.
>
> Thanks,
> Thomas
>
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