@@ -281,14 +281,38 @@ def _run_checked_subprocess(self, command, tex, *, cwd=None):
281281'Failed to process string with tex because {} could not be '
282282'found' .format (command [0 ]))from exc
283283except subprocess .CalledProcessError as exc :
284- raise RuntimeError (
285- '{prog} was not able to process the following string:\n '
286- '{tex!r}\n \n '
287- 'Here is the full report generated by {prog}:\n '
288- '{exc}\n \n ' .format (
289- prog = command [0 ],
290- tex = tex .encode ('unicode_escape' ),
291- exc = exc .output .decode ('utf-8' )))from exc
284+ tex_log = exc .output .decode ('utf-8' )
285+
286+ # whether the exception was likely caused by an unescaped
287+ # underscore. This cannot be easily determined unambiguously.
288+ # By requiring `'$' not in tex` we err on the side of preventing
289+ # false positives, because we only want to issue the customized
290+ # error message if we are sure there's an unescaped underscore.
291+ unescaped_underscore = (
292+ '_' in tex and '$' not in tex and
293+ re .match (r'.*Missing \$ inserted.*_\n' ,tex_log ,
294+ flags = re .DOTALL )
295+ )
296+ if unescaped_underscore :
297+ message = (
298+ '{prog} was not able to process the following string:\n '
299+ '{tex!r}\n \n '
300+ 'This is likely caused by an unescaped underscore.\n '
301+ 'You may escape the underscore or add '
302+ 'r"\\ usepackage{{underscore}}"\n '
303+ 'to the matplotlib rcParam text.latex.preamble' .format (
304+ prog = command [0 ],
305+ tex = tex .encode ('unicode_escape' )))
306+ else :
307+ message = (
308+ '{prog} was not able to process the following string:\n '
309+ '{tex!r}\n \n '
310+ 'Here is the full report generated by {prog}:\n '
311+ '{exc}\n \n ' .format (
312+ prog = command [0 ],
313+ tex = tex .encode ('unicode_escape' ),
314+ exc = tex_log ))
315+ raise RuntimeError (message )from exc
292316_log .debug (report )
293317return report
294318