ENH: make current_backend_module() also ensure one is selected

Author: tacaswell

mpl_gui/__init__.py

@@ -59,9 +59,9 @@ def show(figs, *, block=None, timeout=0):
 
     """
     # TODO handle single figure
-    if _cbm() is None:
-        # set up the backend!
-        select_gui_toolkit()
+
+    # call this to ensure a backend is indeed selected
+    backend = _cbm()
     managers = []
     for fig in figs:
         if fig.canvas.manager is not None:
@@ -78,7 +78,7 @@ def show(figs, *, block=None, timeout=0):
 
     if block and len(managers):
         if timeout == 0:
-            _cbm().Show().mainloop()
+            backend.Show().mainloop()
         elif len(managers):
             manager, *_ = managers
             manager.canvas.start_event_loop(timeout=timeout)

mpl_gui/_manage_backend.py

@@ -3,7 +3,9 @@
 import logging
 
 from matplotlib import cbook, rcsetup
-from matplotlib import rcParamsOrig, rcParams, rcParamsDefault
+from matplotlib import rcParams, rcParamsDefault
+import matplotlib.backend_bases
+
 
 _backend_mod = None
 
@@ -12,8 +14,14 @@
 
 def current_backend_module():
     """
-    Get the currently active backend module
+    Get the currently active backend module, selecting one if needed.
+
+    Returns
+    -------
+    matplotlib.backend_bases._Backend
     """
+    if _backend_mod is None:
+        select_gui_toolkit()
     return _backend_mod