警告：改为将其设置为单个字符串

如何解决警告：改为将其设置为单个字符串

这个警告是什么意思？我怎样才能摆脱这个？

Support for setting the 'text.latex.preamble' or 'pgf.preamble' rcParam to a list of strings is deprecated since 3.3 and will be removed two minor releases later; set it to a single string instead.
  plt.rcParams['text.latex.preamble'] = [r"\usepackage{bm}",[r"\usepackage{amsmath}"]

代码：

import matplotlib.pyplot as plt
plt.rcParams['text.latex.preamble'] = [r"\usepackage{bm}"],[r"\usepackage{amsmath}"]

params = {'text.usetex' : True,'font.size' : 28,'font.family' : 'lmodern',}
plt.rcParams.update(params)

解决方法

根据文档 https://matplotlib.org/3.3.0/api/prev_api_changes/api_changes_3.3.0/deprecations.html#setting-rcparams-text-latex-preamble-default-or-rcparams-pdf-preamble-to-non-strings，将 rcParams['text.latex.preamble'] 设置为字符串列表不再是正确的方法。

要解决此问题，您应该更换

plt.rcParams['text.latex.preamble'] = [r"\usepackage{bm}"],[r"\usepackage{amsmath}"]

成为

plt.rcParams['text.latex.preamble'] = r"\usepackage{bm} \usepackage{amsmath}"