[yt-users] Display variable error?

[Matthew Turk]

Hi Dave,

So I think there are a couple things going on here.  It looks like
this is primarily a matplotlib problem.  If you don't mind not having
any interactive plotting, you should be able to set your
~/.matplotlib/matplotlibrc to have:

backend: Agg

This will prevent pyplot from spawning any X11-mediated widgets, and
it might solve the problem you describe.

If you start an interactive plotting session (which it looks like you
might have) then disconnecting and reconnecting your screen will cause
it to think that it still has access to the underlying toolkit and
widgets it has already instantiated.  The X11 authentication system, I
believe, is resistant to such things -- so even if you were able to
tell matplotlib/pyplot "Hey, my widgets are dead -- can you please
reconstruct them all?" the X11 auth system would argue that it no
longer has privileges to address your screen.  This may be incorrect,
but from my own experience this has been the case.

The second possible approach would be to change the pyplot rendering
engine on the fly.  I don't believe this is possible -- but if you
could start with tkAgg, reconnect somewhere else and switch to Agg,
then you could save to disk and view through an image viewer like xv
or gqview (my favorite.)  If this is possible, your best bet would be
to ask on matplotlib-users. (and then let us know :)

But -- if you're just doing yt-based plots (which you're not here,
from what I can tell) I am pretty sure you can fool yt into changing
rendering engines within a single instantiation of the python
interpreter.  The FigureCanvas is stored in the "engineVals"
dictionary, and changing that would change the output format.

However, all of that aside -- I don't know if Kraken allows VNC
sessions (I'm inclined to suspect they do not.)  If they do, you can
set one up and ssh tunnel to it.  Because they do round-robin login
nodes, this probably won't work.  You might be able to set one up and
then X11 forward a client running remotely, however, which could get
you what you want.

In short: I believe disconnectin/reconnecting with X11 widgets is a
hard problem -- if somebody else knows better, though, I'd be very
grateful to hear.  I tend to do my viz either mediated by
~/public_html/ or through VNC.

-Matt



On Tue, Mar 31, 2009 at 11:13 PM, david collins <antpuncher at gmail.com> wrote:
> Hi, all--
>
> Has anyone seen this error, and do you have a way to get around it
> without re-launching yt?
>
> <error>
>  plt.clf()
>  File "/nics/b/home/collins/local_xt5/lib/python2.6/site-packages/matplotlib/pyplot.py",
> line 336, in clf
>    gcf().clf()
>  File "/nics/b/home/collins/local_xt5/lib/python2.6/site-packages/matplotlib/pyplot.py",
> line 273, in gcf
>    return figure()
>  File "/nics/b/home/collins/local_xt5/lib/python2.6/site-packages/matplotlib/pyplot.py",
> line 251, in figure
>    **kwargs)
>  File "/nics/b/home/collins/local_xt5/lib/python2.6/site-packages/matplotlib/backends/backend_tkagg.py",
> line 90, in new_figure_manager
>    window = Tk.Tk()
>  File "/nics/b/home/collins/local_xt5//lib/python2.6/lib-tk/Tkinter.py",
> line 1643, in __init__
>    self.tk = _tkinter.create(screenName, baseName, className,
> interactive, wantobjects, useTk, sync, use)
> _tkinter.TclError: no display name and no $DISPLAY environment variable
> </error>
>
> I'm running yt on kraken xt5 through a screen session that I have
> re-started after logging out and logging back in.  This has not
> happened on other machines I've done this one.  I tried
> setenv DISPLAY 666.666.6.6:0
> (with the ip of the beast replaced with something real) but it didn't work.
>
> Thanks,
> d.
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