matplotlib
diff --git a/‎lib/matplotlib/__init__.py
Copy file name to clipboardExpand all lines: lib/matplotlib/__init__.py
+4Lines changed: 4 additions & 0 deletions b/‎lib/matplotlib/__init__.py
Copy file name to clipboardExpand all lines: lib/matplotlib/__init__.py
+4Lines changed: 4 additions & 0 deletions
@@ -849,6 +849,10 @@ def __setitem__(self, key, val):
                 cbook.warn_deprecated(
                     "3.0", "{} is deprecated; in the future, examples will be "
                     "found relative to the 'datapath' directory.".format(key))
+            elif key == 'backend':
+                if val is rcsetup._auto_backend_sentinel:
+                    if 'backend' in self:
+                        return
             try:
                 cval = self.validate[key](val)
             except ValueError as ve: