Defer checking of tex install to when it is actually used. (#13285)

anntzer · timhoffm · commit d7c6c5b2e305 · 2019-01-28T22:35:54.000+01:00
The call to checkdep_usetex() in `__init__.py` doesn't help for people
explicitly passing usetex=True.  Moreover, it slows down import time
for those who *do* have text.usetex set to True in their rcfile by ~20ms
(when timing this, note that checkdep_ghostscript (which checkdep_usetex
calls) has a cache, which should be disabled for timing purposes.

Moreover, checkdep_usetex is overly broad, always requiring dvipng
(which is not required for pdf/ps output) and ghostscript (which is not
required for raster output).

Instead, move the check to texmanager.py, which will provide a more
meaningful error message to end users, speed up import time (20ms is
similar to the import time of pyparsing or urllib.request, for example)
and avoid the inaccuracies above.
diff --git a/lib/matplotlib/__init__.py b/lib/matplotlib/__init__.py
@@ -968,8 +968,6 @@ def rc_params_from_file(fname, fail_on_error=False, use_default_template=True):
 rcParams['ps.usedistiller'] = checkdep_ps_distiller(
                       rcParams['ps.usedistiller'])
 
-rcParams['text.usetex'] = checkdep_usetex(rcParams['text.usetex'])
-
 if rcParams['axes.formatter.use_locale']:
     locale.setlocale(locale.LC_ALL, '')
 
diff --git a/lib/matplotlib/texmanager.py b/lib/matplotlib/texmanager.py
@@ -302,6 +302,10 @@ def _run_checked_subprocess(self, command, tex):
             report = subprocess.check_output(command,
                                              cwd=self.texcache,
                                              stderr=subprocess.STDOUT)
+        except FileNotFoundError as exc:
+            raise RuntimeError(
+                'Failed to process string with tex because {} could not be '
+                'found'.format(command[0])) from exc
         except subprocess.CalledProcessError as exc:
             raise RuntimeError(
                 '{prog} was not able to process the following string:\n'
@@ -310,7 +314,7 @@ def _run_checked_subprocess(self, command, tex):
                 '{exc}\n\n'.format(
                     prog=command[0],
                     tex=tex.encode('unicode_escape'),
-                    exc=exc.output.decode('utf-8')))
+                    exc=exc.output.decode('utf-8'))) from exc
         _log.debug(report)
         return report
 
