[Matplotlib-users] Error when saving as PDF using $\alpha$ and 'text.usetex':True

Hi:

I am getting an error when I save a figure as PDF with a particular
configuration and when I use a greek latex leter (say $\alpha$) as a
ylabel. The following code illustrates the problem.

###############################################
import matplotlib.pyplot as plt
import matplotlib as mpl

params = {
    'text.usetex' : True,
    'font.family': 'serif',
    'font.serif' : ['Times'],
    }
mpl.rcParams.update(params)

plt.figure()
plt.plot([1,2,3])
plt.ylabel(r'$\alpha$')
plt.savefig('f1.pdf')
###############################################

When I run it I get

Traceback (most recent call last):
  File "multipage_pdf.py", line 14, in <module>
    plt.savefig('f1.pdf')
  File "/usr/local/lib/python2.7/dist-packages/matplotlib/pyplot.py",
line 472, in savefig
    return fig.savefig(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/matplotlib/figure.py",
line 1173, in savefig
    self.canvas.print_figure(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/matplotlib/backend_bases.py",
line 2027, in print_figure
    **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/matplotlib/backend_bases.py",
line 1799, in print_pdf
    return pdf.print_pdf(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_pdf.py",
line 2187, in print_pdf
    file.close()
  File "/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_pdf.py",
line 470, in close
    self.writeFonts()
  File "/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_pdf.py",
line 557, in writeFonts
    fonts[Fx] = self.embedTeXFont(filename, self.dviFontInfo[filename])
  File "/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_pdf.py",
line 622, in embedTeXFont
    t1font = t1font.transform(fontinfo.effects)
  File "/usr/local/lib/python2.7/dist-packages/matplotlib/type1font.py",
line 301, in transform
    buffer.write(value)
TypeError: unicode argument expected, got 'str'


Note that with any of the following variations the code works as expected:

- If I use plt.ylabel(r'$x_2$') instead of plt.ylabel(r'$\alpha$).
- If I save as PNG instead of PDF.
- Use the default configuration (comment the mpl.rcParams.update(params) line).

I am using MPL verion 1.2.x (built from commit 396a6446).

Am I doing something wrong? Any idea how to solve it?

Alejandro.