PGF preamble is not used

Commencez par l’affectation de rcParams dans Julia et la frontière PyCall, puis comparez la valeur qui atteint le backend PGF de Matplotlib avec l’exemple Python fonctionnel et le traceback de backend_pgf.py présenté ici. Reproduisez l’exemple et vérifiez que la macro LaTeX définie est disponible pendant le rendu de la figure et que test.pdf est généré avec succès.

I am trying to define macros in my "pgf.preamble" so I can later change parts of the figure labels when including my figures in a LaTeX document without having to regenerate the figures. This works well in python:

import numpy as np
import matplotlib
import matplotlib.pyplot as plt

matplotlib.use("pgf")

plt.rcParams.update({
    "text.usetex": True,
    "pgf.preamble": "\n".join([
        r"\newcommand{\cmd}{t_a}",
    ])
})

x = np.linspace(0, 10, 100)
y = np.sin(x)

fig, ax = plt.subplots()
ax.plot(x, y, label=r"$\sin(x)$")
ax.legend()
ax.set_ylabel(L"$\cmd$")
fig.savefig("test.pdf")

runs and correctly puts $t_a$ into the y-label of the output PDF. In julia on the other hand:

using PyPlot

PyPlot.matplotlib.use("pgf")
rcParams = PyPlot.PyDict(PyPlot.matplotlib."rcParams")
rcParams["pgf.preamble"] = [
                            raw"\newcommand{\cmd}{t_a}"
                            ]
rcParams["text.usetex"] = true
x = 0:0.1:10
y = sin.(x)
fig, ax = PyPlot.subplots()
ax.plot(x, y, label=L"$\sin(x)$")
ax.legend()
ax.set_ylabel(L"$\cmd$")
fig.savefig("test.pdf")

fails in the last line with

ERROR: PyError ($(Expr(:escape, :(ccall(#= /home/yc20910/.julia/packages/PyCall/1gn3u/src/pyfncall.jl:43 =# @pysym(:PyObject_Call), PyPtr, (PyPtr, PyPtr, PyPtr), o, pyargsptr, kw))))) <class 'ValueError'>
ValueError("Error measuring '\\\\sffamily\\\\fontsize{10.000000}{12.000000}\\\\selectfont \\\\(\\\\displaystyle \\\\cmd\\\\)'\nLaTeX Output:\n! Undefined control sequence.\n<argument> ...00}\\selectfont \\(\\displaystyle \\cmd \n                                                  \\)\n<*> ....000000}\\selectfont \\(\\displaystyle \\cmd\\)}\n                                                  \\typeout{\\the\\wd0,\\the\\ht0...\nNo pages of output.\nTranscript written on texput.log.\n")
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/figure.py", line 3012, in savefig
    self.canvas.print_figure(fname, **kwargs)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/backend_bases.py", line 2314, in print_figure
    result = print_method(
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/backends/backend_pgf.py", line 873, in print_pdf
    self.print_pgf(tmppath / "figure.pgf", **kwargs)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/backends/backend_pgf.py", line 860, in print_pgf
    self._print_pgf_to_fh(file, **kwargs)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/backend_bases.py", line 1643, in wrapper
    return func(*args, **kwargs)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/backends/backend_pgf.py", line 845, in _print_pgf_to_fh
    self.figure.draw(renderer)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/artist.py", line 73, in draw_wrapper
    result = draw(artist, renderer, *args, **kwargs)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/artist.py", line 50, in draw_wrapper
    return draw(artist, renderer)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/figure.py", line 2803, in draw
    mimage._draw_list_compositing_images(
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/image.py", line 132, in _draw_list_compositing_images
    a.draw(renderer)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/artist.py", line 50, in draw_wrapper
    return draw(artist, renderer)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/axes/_base.py", line 3082, in draw
    mimage._draw_list_compositing_images(
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/image.py", line 132, in _draw_list_compositing_images
    a.draw(renderer)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/artist.py", line 50, in draw_wrapper
    return draw(artist, renderer)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/axis.py", line 1172, in draw
    self.label.draw(renderer)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/artist.py", line 50, in draw_wrapper
    return draw(artist, renderer)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/text.py", line 685, in draw
    bbox, info, descent = self._get_layout(renderer)
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/text.py", line 317, in _get_layout
    w, h, d = renderer.get_text_width_height_descent(
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/backends/backend_pgf.py", line 738, in get_text_width_height_descent
    w, h, d = (LatexManager._get_cached_or_new()
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/backends/backend_pgf.py", line 334, in get_width_height_descent
    return self._get_box_metrics(_escape_and_apply_props(text, prop))
  File "/home/yc20910/.local/lib/python3.8/site-packages/matplotlib/backends/backend_pgf.py", line 347, in _get_box_metrics
    raise ValueError("Error measuring {!r}\nLaTeX Output:\n{}"

Stacktrace:
  [1] pyerr_check
    @ ~/.julia/packages/PyCall/1gn3u/src/exception.jl:75 [inlined]
  [2] pyerr_check
    @ ~/.julia/packages/PyCall/1gn3u/src/exception.jl:79 [inlined]
  [3] _handle_error(msg::String)
    @ PyCall ~/.julia/packages/PyCall/1gn3u/src/exception.jl:96
  [4] macro expansion
    @ ~/.julia/packages/PyCall/1gn3u/src/exception.jl:110 [inlined]
  [5] #107
    @ ~/.julia/packages/PyCall/1gn3u/src/pyfncall.jl:43 [inlined]
  [6] disable_sigint
    @ ./c.jl:473 [inlined]
  [7] __pycall!
    @ ~/.julia/packages/PyCall/1gn3u/src/pyfncall.jl:42 [inlined]
  [8] _pycall!(ret::PyCall.PyObject, o::PyCall.PyObject, args::Tuple{String}, nargs::Int64, kw::Ptr{Nothing})
    @ PyCall ~/.julia/packages/PyCall/1gn3u/src/pyfncall.jl:29
  [9] _pycall!
    @ ~/.julia/packages/PyCall/1gn3u/src/pyfncall.jl:11 [inlined]
 [10] (::PyCall.PyObject)(args::String)
    @ PyCall ~/.julia/packages/PyCall/1gn3u/src/pyfncall.jl:86
 [11] top-level scope
    @ REPL[41]:1