未知的符号matplotlib mathtext

Question

我正在尝试使用mathtext正确渲染我的图形轴标签（理想情况下我不想使用Latex本身来渲染文本）。但是，这个小的最小工作示例会产生如下所示的错误。在我看来它应该工作，可能是一个没有安装的必要包？

我正在运行matplotlib 2.2.2和Python 3.5

import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(1,1,1)
ax.plot(0,0)
ax.set_ylabel(r'$\mathrm A$')

产生的错误：

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/mathtext.py", line 2516, in parse
    result = self._expression.parseString(s)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1632, in parseString
    raise exc
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1622, in parseString
    loc, tokens = self._parse( instring, 0 )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1529, in _parseCache
    value = self._parseNoCache(instring, loc, doActions, callPreParse)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1379, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 3717, in parseImpl
    return self.expr._parse( instring, loc, doActions, callPreParse=False )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1529, in _parseCache
    value = self._parseNoCache(instring, loc, doActions, callPreParse)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1379, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 3395, in parseImpl
    loc, exprtokens = e._parse( instring, loc, doActions )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1529, in _parseCache
    value = self._parseNoCache(instring, loc, doActions, callPreParse)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1379, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 3919, in parseImpl
    return super(ZeroOrMore, self).parseImpl(instring, loc, doActions)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 3848, in parseImpl
    loc, tokens = self_expr_parse( instring, loc, doActions, callPreParse=False )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1529, in _parseCache
    value = self._parseNoCache(instring, loc, doActions, callPreParse)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1379, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 3378, in parseImpl
    loc, resultlist = self.exprs[0]._parse( instring, loc, doActions, callPreParse=False )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1529, in _parseCache
    value = self._parseNoCache(instring, loc, doActions, callPreParse)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1405, in _parseNoCache
    tokens = fn( instring, tokensStart, retTokens )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1049, in wrapper
    ret = func(*args[limit[0]:])
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/mathtext.py", line 2585, in math_string
    return self._math_expression.parseString(toks[0][1:-1])
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1632, in parseString
    raise exc
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1622, in parseString
    loc, tokens = self._parse( instring, 0 )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1529, in _parseCache
    value = self._parseNoCache(instring, loc, doActions, callPreParse)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1379, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 3717, in parseImpl
    return self.expr._parse( instring, loc, doActions, callPreParse=False )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1529, in _parseCache
    value = self._parseNoCache(instring, loc, doActions, callPreParse)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1379, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 3848, in parseImpl
    loc, tokens = self_expr_parse( instring, loc, doActions, callPreParse=False )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1529, in _parseCache
    value = self._parseNoCache(instring, loc, doActions, callPreParse)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1379, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 3717, in parseImpl
    return self.expr._parse( instring, loc, doActions, callPreParse=False )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1529, in _parseCache
    value = self._parseNoCache(instring, loc, doActions, callPreParse)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1379, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 3530, in parseImpl
    ret = e._parse( instring, loc, doActions )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1529, in _parseCache
    value = self._parseNoCache(instring, loc, doActions, callPreParse)
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1405, in _parseNoCache
    tokens = fn( instring, tokensStart, retTokens )
  File "/usr/local/lib/python3.5/dist-packages/pyparsing.py", line 1049, in wrapper
    ret = func(*args[limit[0]:])
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/mathtext.py", line 2687, in unknown_symbol
    raise ParseFatalException(s, loc, "Unknown symbol: %s" % c)
pyparsing.ParseFatalException: Unknown symbol: \mathrm (at char 0), (line:1, col:1)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/backends/backend_gtk3agg.py", line 39, in on_draw_event
    self._render_figure(w, h)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/backends/backend_gtk3agg.py", line 30, in _render_figure
    backend_agg.FigureCanvasAgg.draw(self)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/backends/backend_agg.py", line 433, in draw
    self.figure.draw(self.renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/artist.py", line 55, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/figure.py", line 1475, in draw
    renderer, self, artists, self.suppressComposite)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/image.py", line 141, in _draw_list_compositing_images
    a.draw(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/artist.py", line 55, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/axes/_base.py", line 2607, in draw
    mimage._draw_list_compositing_images(renderer, self, artists)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/image.py", line 141, in _draw_list_compositing_images
    a.draw(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/artist.py", line 55, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/axis.py", line 1204, in draw
    self.label.draw(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/artist.py", line 55, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/text.py", line 706, in draw
    bbox, info, descent = textobj._get_layout(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/text.py", line 309, in _get_layout
    ismath=ismath)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/backends/backend_agg.py", line 237, in get_text_width_height_descent
    self.mathtext_parser.parse(s, self.dpi, prop)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/mathtext.py", line 3294, in parse
    box = self._parser.parse(s, font_output, fontsize, dpi)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/mathtext.py", line 2522, in parse
    six.text_type(err)]))
ValueError: 
\mathrm A
^
Unknown symbol: \mathrm (at char 0), (line:1, col:1)

If you suspect this is an IPython bug, please report it at:
    https://github.com/ipython/ipython/issues
or send an email to the mailing list at ipython-dev@python.org

You can print a more detailed traceback right now with "%tb", or use "%debug"
to interactively debug it.

Extra-detailed tracebacks for bug-reporting purposes can be enabled via:
    %config Application.verbose_crash=True

Answer 1

你是正确的，在LaTeX中，\mathrm A是有效的，但不要忘记Matplotlib解析器与LaTeX不同。

我在Python 3.6.4和Matplotlib 2.2.2上尝试了这个，错误不再存在。