Unicode error using matplotlib with log scale on Windows

Question

I'm using python 2.6 and matplotlib. If I run the sample histogram_demo.py provided in the matplotlib gallery page, it works fine. I've simplified this script greatly:

import numpy as np
import matplotlib.pyplot as plt

mu, sigma = 100, 15
x = mu + sigma * np.random.randn(10000)

fig = plt.figure()
ax = fig.add_subplot(111)

n, bins, patches = ax.hist(x, 50, normed=1, facecolor='green', alpha=0.75)

ax.set_yscale('log')  # <---- add this line to generate the error
plt.show()

I get this error (at the plt.show() line):

TypeError: coercing to Unicode: need string or buffer, dict found

I've tried changing the backend to many different values - nothing helps. I am using Qt4Agg. Is this a font issue? It seems that it must be something with my configuration. Note: Because of other problems, I just installed a fresh copy of python26, matplotlib, numpy, scipy. I have another XP-box running python26 and it executes both versions of the script with no errors. I hope someone can help. Many thanks in advance.

Answer 1

This is a bug in the font management of matplotlib, on my machine this is the file /usr/lib/pymodules/python2.6/matplotlib/font_manager.py:1220. I've highlighted the change in the code snippet below; this is fixed in the newest version of matplotlib.

if best_font is None or best_score >= 10.0:
    verbose.report('findfont: Could not match %s. Returning %s' %
                       (prop, self.defaultFont))
    [+]result = self.defaultFont[fontext]
    [-]result = self.defaultFont
    print "defaultFont", result
else:
    verbose.report('findfont: Matching %s to %s (%s) with score of %f' %
                       (prop, best_font.name, best_font.fname, best_score))
    result = best_font.fname
    print "best_font", result

This error occurs only if no "good" font was found and the font manager falls back to a default font. Therefore the error occured without apparent reason, probably because of changes in the installed fonts.

Hope that helps!

Answer 2

I had the same problem with matplotlib 0.98.5.2. I was able to fix it by upgrading to matplotlib 1.0.1 (0.99.3 didn't work), or by blowing away my ~/.matplotlib directory. Not sure what the equivalent is for Windows.

Answer 3

I had the same problem today, and I found the issue in github

https://github.com/matplotlib/matplotlib/issues/198

The proposed workaround is to delete the .matplotlib/fontList.cache file, and worked for me.