Python Headless MatplotLib / Pyplot [duplicate]

Question

I'm trying to make my data analysis and reports less eye stabbing and more graphical with automatically generated graph-files, and to do this I've been playing with matplotlib/pyplot/pylab. Works brilliantly, but when I try to run it on a headless server...

tkinter.TclError: no display name and no $DISPLAY environment variable 

For this application I only use PyLab, but after a little google, I added the below to before the pylab import:

import matplotlib matplotlib.use("Agg") 

Which should have changed the backend, but to no effect.

Any ideas what I'm doing wrong?

The remote machine does have X-forwarding capabilities, but since this application shouldn't NEED to display anything, I believe the usual ssh -X hack is overkill.

Examples:Fiendish Deception

Example working code on same machine

import matplotlib matplotlib.use("Agg") import numpy as np import pylab as pl   xvals=np.arange(100) yvals=np.cumsum(np.random.random(100)) yvals[-10:]=0 yvals=np.log(yvals) pl.close()  pl.plot(xvals,yvals) pl.xlabel("X") pl.ylabel("Y") pl.title("Title")  pl.savefig("testgraph.png") 

Non-working real code

import matplotlib matplotlib.use("Agg") import numpy as np import pylab as pl import utility as util import os  ... non graph stuff... def graph_p(self):     pl.close()     channels=range(self.p.shape[0])     for line in range(self.p.shape[1]):         yvals=np.ma.masked_invalid(map(util.watts_to_dbmhz,self.p[:,line]))         pl.plot(channels,yvals) #Error says it occurs here     pl.xlabel("Subchannel Index")     pl.ylabel("Power (dbmhz)")     pl.title("Plot of per-tone power assignments for %d lines"%self.p.shape[1])     pl.savefig(self.dest+self.scenario+'-power.png') 

Nothing else touches pyplot.

Answer 1

Everything you describe sounds correct. What happens when you run this:

import matplotlib matplotlib.use('Agg') import pylab pylab.plot([1,2], [3,4], linestyle='-') pylab.savefig('foo.png') 

In my environment it produces this (I scaled it down):