matplotlib - savefig with usetex=True - matplotlib

Question

I am having problems saving a figure created by matplotlib as a .eps or .ps when I enable usetex=True. This works when this is not enabled. Here's an example:
plt.plot([1,2,3], [1,2,3], 'b.')
plt.text(2,2,r'\textbf{(a)} \lambda_{1} value', usetex=True, fontsize=16, fontname='Times New Roman')
plt.savefig('check.eps')
I receive this error:
File "C:\Python27\lib\site-packages\matplotlib\backends\backend_ps.py", line 671, in draw_tex
thetext = 'psmarker%d' % self.textcnt
AttributeError: 'RendererPS' object has no attribute 'textcnt'
I also cannot set the font to Time New Roman using the text command when I enable usetex=True.

Answer 1

Even if it is a bit late, I would like to give an answer, if someone else searches for this error.
Saving eps files starts the RendererPS backend, which checks whether plt.rcParams['text.usetex'] is set to True to initialise its textcnt attribute. Since usetex is set only for the text object, the backend does not expect to have to handle LaTeX and throws an error when it tries to. These kind of inconsistencies concerning LaTeX rendering are sadly present in a number of places in matplotlib.
If you cannot achieve the text formatting with the standard matplotib functionality, one solution is to set usetex globally: plt.rcParams['text.usetex'] = True. This render all the text of the figure with LaTeX (e.g. also tick labels or axis labels). I would recommend to do this in any case, to have consistent visuals.
Concerning the font, the fontname argument only affects standard matplotlib formatting. For LaTeX rendering, you have to specify the font like you would do in LaTeX. To get a font like Times New Roman, you need to load the respective package e.g. mathptmx (the times package is deprecated) by plt.rcParams['text.latex.preamble'] = [r'\usepackage{mathptmx}']. Of course, the package has to be installed in your local LaTeX installation. The standard font family in matplotlib is sans-serif, so this has to be changed to serif with plt.rcParams['font.family'] = 'serif'.
The final code is:
import matplotlib.pyplot as plt
# LaTeX setup
plt.rcParams['text.latex.preamble'] = [r'\usepackage{mathptmx}'] # load times roman font
plt.rcParams['font.family'] = 'serif' # use serif font as default
plt.rcParams['text.usetex'] = True # enable LaTeX rendering globally
plt.plot([1,2,3], [1,2,3], 'b.')
plt.text(2,2,r'\textbf{(a)} $\lambda_1$ value', fontsize=16)
plt.savefig('check.eps')
Note, that you have to enclose the math variable in dollar signs $\lambda_1$, otherwise you get an error or warning in LaTeX. (Also, single character subscripts do not need to be enclosed in curly brackets).
As a side note: I encountered the same error, when trying to save a figure as eps after turning usetex off again.