Warn if a temporary config/cache dir must be created.

anntzer · anntzer · commit a19d9c59ee01 · 2019-12-15T14:52:55.000+01:00
Paying the cost of regen'ing the font cache on every import seems a bit
silly when one can just set MPLCONFIGDIR to a persistent directory.
Moreover the tmpdir approach is brittle against forking; this is fixable
but somewhat complex to do.
diff --git a/lib/matplotlib/__init__.py b/lib/matplotlib/__init__.py
@@ -519,16 +519,6 @@ def get_home():
         return None
 
 
-def _create_tmp_config_or_cache_dir():
-    """
-    If the config or cache directory cannot be created, create a temporary one.
-    """
-    configdir = os.environ['MPLCONFIGDIR'] = (
-        tempfile.mkdtemp(prefix='matplotlib-'))
-    atexit.register(shutil.rmtree, configdir)
-    return configdir
-
-
 def _get_xdg_config_dir():
     """
     Return the XDG configuration directory, according to the `XDG
@@ -562,7 +552,17 @@ def _get_config_or_cache_dir(xdg_base):
     else:
         if os.access(str(configdir), os.W_OK) and configdir.is_dir():
             return str(configdir)
-    return _create_tmp_config_or_cache_dir()
+    # If the config or cache directory cannot be created or is not a writable
+    # directory, create a temporary one.
+    tmpdir = os.environ["MPLCONFIGDIR"] = \
+        tempfile.mkdtemp(prefix="matplotlib-")
+    atexit.register(shutil.rmtree, tmpdir)
+    _log.warning(
+        "Matplotlib created a temporary config/cache directory at %s because "
+        "the default path (%s) is not a writable directory; it is recommended "
+        "to set the MPLCONFIGDIR environment variable to a writable "
+        "directory.", configdir, tmpdir)
+    return tmpdir
 
 
 @_logged_cached('CONFIGDIR=%s')
