add qt config option to clear_on_kernel_restart

[ivanov]

Previously, restarting a kernel in the qtconsole always cleared the
entire session. Since qtconsole has a %clear command, it makes sense to
allow users to decouple the two activities - the restarting of kernels,
and clearing the console. This PR adds a configuration option which allows for the restarting of kernels without losing console history. The default value for clear_on_kernel_restart is set to True to stay consistent with the way things worked before this functionality was added.

To test, run:

ipython qtconsole --IPythonWidget.clear_on_kernel_restart=False

Here's what it looks like when the user restarts the kernel on In[3]:

Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41)
Type "copyright", "credits" or "license" for more information.

IPython 0.13.dev -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.
%guiref   -> A brief reference about the graphical user interface.

In [1]: 0x42
Out[1]: 66

In [2]: 042
Out[2]: 34

In [3]: # restarting kernel...
#------------------------------------------

In [1]:

[ivanov]

I could use feedback if I should go ahead and remove the messagebox logic on after line 522 to also use this new option.

[fperez]

No time to review right now (gotta catch a flight early tomorrow, will be offline for a bit), but I wanted to say thank you for this. I've been wanting this for a long time.

[takluyver]

IIRC, we're using a rich text widget - is it easy to draw a proper horizontal line, rather than an ASCII art -----?

[ivanov]

ok, now using html <hr> instead of ASCII ----, took me a bit to get to the bottom of it, so @takluyver better be happy with the results! ;)

[takluyver]

Thanks Paul, I've just tested, and I like the way it's looking now.

[minrk]

Looks good to me. Any reason not to merge?

[ivanov]

@minrk, actually, yeah, hang on, found a minor problem with this

[ivanov]

ok @minrk and @takluyver - I think it's ready to merge again:

I originally made a new method (reset_on_restart) to accommodate this
new functionality, but it turns out I ended up needing to replicate
almost everything that reset() already does inside this new method. In
particular, reset_on_restart did not work properly when restarting a
kernel that was in debug mode.

Everything should now work, and we don't have another method to deal
with.

[ivanov]

having second thoughts about calling the parameter force, does clear make more sense? or force_clear?

[minrk]

clear seems most appropriate, since that's the switch you are flipping.

[takluyver]

I agree that clear makes more sense - force sounds like "don't ask for confirmation".

Other than that, it looks good, and I think putting it inside the reset method makes sense. I assume you've tested it again in both modes.

[ivanov]

ok, thanks for being patient with me, guys. Renamed it to clear, ready to merge, and yes, tested it in both modes.

[SamuelDeleglise]

Hi all,

I am not sure if this is the best place for this comment, but I will try anyway:
I use ipython notebook (IPython 2.1.0) on windows. The options are interpreted correctly (for instance launching the notebook with --IPythonWidget.confirm_restart=False has the correct effect), however, the option IPythonWidget.clear_on_kernel_restart=True has no effect. This is particularly cumbersome since there is a small bug associated with restarting the kernel without clearing the screen: the console doesn't scroll down to the first command prompt (it scrolls down only to the horizontal line, and I have to hit enter once to have it scroll to the new command prompt).

Are these 2 bugs (scrolling problem + no way to disable clear_on_kernel_restart) windows related and is there a way to solve them? I use the pythonxy distribution and these problems have been appearing on all the computers I have tried so far.

Thanks for your help,
Samuel

[takluyver]

Hi Samuel - it looks like the code to check that option was taken out somewhere along the line. If you can work out where it should be checked, please make a pull request to do so.

[SamuelDeleglise]

Hi Thomas, Thanks for the quick reply, I have been looking around in the code, especially in
IPython\qt\console\frontend_widget.py
Hoping for a commented line or something as trivial as that, but after one hour of digging, I must admit my incompetence. I tried to add a self.reset(True) in restart_kernel(..) but I have the feeling it's actually restarting the kernel twice since the restart command is taking very long...
Sorry for not being more helpful,
Cheers,
Samuel

[takluyver]

It certainly looks like sticking self.reset(True) in the right part of restart_kernel (about where it adds the "Restarting kernel..." HTML) should work.