Display message from TryNext error in magic_paste

[takluyver]

If you do %paste on a system without Tkinter installed, this makes sure you get the more informative error message.

Closes gh-1736

[bfroehle]

This changes the behavior slightly, as before we'd guarantee the exception's args and kw attributes would be as passed to __call__, but now we only take the results from the raised exception (which likely have args = (), and kw = {}).

Is the ability of the exception to change the calling arguments ever actually used? I can't seem to find an instance of this in the IPython source.

[takluyver]

At a quick look, here and in magic_paste are the only code where TryNext is caught and captured. I think the ability to change args/kwargs is intended to act within CommandChainDispatcher, not to propagate to calling code, and this doesn't affect that. But no, I don't think it's actually used at all. It's hard to see a use case that maintains weak coupling. Maybe it should just be ditched...

[bfroehle]

I think we should consider removing the args/kw capability in TryNext. It's been present, in its current form, since the dawn of time (or at least since 2f09c2a which is the start of the history in git).

[takluyver]

OK, let's take this to the mailing list. I'll make a post about it.

[bfroehle]

Certainly the PR works:

In [1]: import sys; sys.modules['Tkinter'] = None

In [2]: paste
ERROR: Getting text from the clipboard on this platform requires Tkinter.

[Carreau]

@takluyver,
nobody seem to have complained, do you want to fix the conflict and merge ?

[bfroehle]

Started a branch for this: https://github.com/bfroehle/ipython/compare/_1736_try_next

Haven't tested it, but can open a pull request later this evening.

[takluyver]

@bfroehle : At a glance, that branch looks good, so go for a pull request. I'm with my family for a long weekend, so I'm checking email, but I don't have much time to actually code.

[takluyver]

Superseded by #1850 - closing.