matplotlib pgf backend with lualatex - non-math font does not change

Question

When using Python's matplotlib to produce plots, I sometimes require the lualatex engine using the pgf backend for matplotlib when producing "heavier" plots like hexbin, otherwise the TeX memory is exceeded and pdflatex fails. When using lualatex The math font seems to change according to my pgf.preamble, however, the rest of the font does not, and stays as CM Roman. With pdflatex, the font behaves how I want. Note that if I go to www.overleaf.com and use the same preamble and compile with pdflatex or lualatex, the document shows the fonts I desire, in both math, and main body. EDIT: the main body font actually does not work in overleaf, I was mistaken.

Update: xelatex behaves the same as lualatex, ie. only math fonts are changed.

Update: Solved by using \usepackage{fontspec}\usepackage[T1]{fontenc} at the start of the preamble. I thought fontspec would not do anything with the T1 font encoding, but it's needed and it works.

This question is similar to: How do I use kpfonts with fontspec?

With lua engine:

with pdf engine:

Code:

import matplotlib as mpl

eng = 'lua' # issue with lua only   <<<<<<<<
# eng = 'pdf' # no issue here
# eng = 'xe' # update: issue here as well

mpl.use('pgf')
mpl.rc('font', family='serif')
mpl.rcParams.update({
        "pgf.rcfonts"  : False,
        "pgf.texsystem": eng + "latex",
        "pgf.preamble" : '\\usepackage[utf8x]{inputenc}\\usepackage[light]{kpfonts}',
})

import numpy as np
import matplotlib.pyplot as plt

t = np.linspace(0,6,100)
x = np.sin(t)

fig, ax = plt.subplots()
ax.plot(t, x, label='A line')
plt.title('A function, $f(x) = \sin(x)$')
plt.legend()
plt.savefig('example.pdf')

Answer 1

What happens if you remove the preamble settings and change example.pdf to example.pgf?. Or is there a reason to use pdf-format?

When I render something in Matplotlib that will be put into Latex, I always choose render with Latex and maybe set some basic settings like (sans-)serif and font size, and choose the output format to be pgf.

Doing this and choosing not to set the explicit font, I can later switch fonts without having to render another figure. This is because the actual plot will be plotted when rendering the pdf from Latex (in your case, when you click "Compile" in Overleaf).

If you do this, I think you have to change \includegraphics{example.pdf} to \input{example.pgf}, since it is LaTeX-code you want to include.

Answer 2

Set "pgf.preamble" to:

\usepackage{fontspec}
\usepackage[T1]{fontenc}
\usepackage[utf8x]{inputenc}
\usepackage[light]{kpfonts}

See: How do I use kpfonts with fontspec?