class_docstr: Convert strings to dvi files using TeX, caching the results to a directory.
  
  The cache directory is called ``tex.cache`` and is located in the directory
  returned by `.get_cachedir`.
  
  Repeated calls to this constructor always return the same instance.
class_docstr_tok: ["Convert","strings","to","dvi","files","using","TeX",",","caching","the","results","to","a","directory",".","The","cache","directory","is","called","``","tex.cache","``","and","is","located","in","the","directory","returned","by","`",".get_cachedir","`",".","Repeated","calls","to","this","constructor","always","return","the","same","instance","."]
docstr: Return a string containing font configuration for the tex preamble.
docstr_tok: ["Return","a","string","containing","font","configuration","for","the","tex","preamble","."]
code: def get_font_preamble(cls):
      """
      Return a string containing font configuration for the tex preamble.
      """
      font_preamble, command = cls._get_font_preamble_and_command()
      return font_preamble
  
imports: import functools
  import hashlib
  import logging
  import os
  from pathlib import Path
  import subprocess
  from tempfile import TemporaryDirectory
  import numpy
  import matplotlib
  from matplotlib import _api, cbook, dviread
label_desc: Use image node_id 5 for calling the TexManager obj's underlying member method code with example usage: obj.get_font_preamble(cls) and returns: font_preamble