Avoid calling vars() on arbitrary third-party manager_class.

vars(...) may fail if the third-party manager_class has no `__dict__`,
which can happen in contrieved cases involving `__slots__` or extension
modules, or more simply if the backend has no FigureCanvas attribute or
if the canvas class has no manager_class attribute, in which case
manager_class = None.  (Note that this can only be the case if that
third-party FigureCanvas doesn't inherit from FigureCanvasBase, which is
probably not a great idea.)

In any case, instead of vars(), inspect.getattr_static does what we want
too and also handles that case.

Also replace another (unrelated) use of vars() with a plain getattr.

Author: anntzer

lib/matplotlib/backends/backend_qt.py

@@ -898,7 +898,7 @@ def _tight_layout(self):
         self._figure.tight_layout()
         for attr, spinbox in self._spinboxes.items():
             spinbox.blockSignals(True)
-            spinbox.setValue(vars(self._figure.subplotpars)[attr])
+            spinbox.setValue(getattr(self._figure.subplotpars, attr))
             spinbox.blockSignals(False)
         self._figure.canvas.draw_idle()
 

lib/matplotlib/pyplot.py

@@ -324,11 +324,12 @@ def draw_if_interactive():
     # show is already present, as the latter may be here for backcompat.
     manager_class = getattr(getattr(backend_mod, "FigureCanvas", None),
                             "manager_class", None)
-    # We can't compare directly manager_class.pyplot_show and FMB.pyplot_show
-    # because pyplot_show is a classmethod so the above constructs are bound
-    # classmethods, & thus always different (being bound to different classes).
-    manager_pyplot_show = vars(manager_class).get("pyplot_show")
-    base_pyplot_show = vars(FigureManagerBase).get("pyplot_show")
+    # We can't compare directly manager_class.pyplot_show and FMB.pyplot_show because
+    # pyplot_show is a classmethod so the above constructs are bound classmethods, and
+    # thus always different (being bound to different classes).  We also have to use
+    # getattr_static instead of vars as manager_class could have no __dict__.
+    manager_pyplot_show = inspect.getattr_static(manager_class, "pyplot_show", None)
+    base_pyplot_show = inspect.getattr_static(FigureManagerBase, "pyplot_show", None)
     if (show is None
             or (manager_pyplot_show is not None
                 and manager_pyplot_show != base_pyplot_show)):