Also update the backend when doing rcParams["backend"] = "foo".

anntzer · anntzer · commit 307c1ecf5d8f · 2017-12-06T21:54:26.000-08:00
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -262,13 +262,28 @@ def validate_backend(s):
         lambda s:
         s if s.startswith("module://")
         else ValidateInStrings('backend', all_backends, ignorecase=True)(s))(s)
+    pyplot = sys.modules.get("matplotlib.pyplot")
     if len(candidates) == 1:
-        return candidates[0]
+        backend, = candidates
+        if pyplot:
+            # This import needs to be delayed (below too) because it is not
+            # available at first import.
+            from matplotlib import rcParams
+            # Don't recurse.
+            old_backend = rcParams["backend"]
+            if old_backend == backend:
+                return backend
+            dict.__setitem__(rcParams, "backend", backend)
+            try:
+                pyplot.switch_backend(backend)
+            except Exception:
+                dict.__setitem__(rcParams, "backend", old_backend)
+                raise
+        return backend
     else:
-        pyplot = sys.modules.get("matplotlib.pyplot")
         if pyplot:
-            pyplot.switch_backend(candidates)  # Actually resolves the backend.
             from matplotlib import rcParams
+            pyplot.switch_backend(candidates)  # Actually resolves the backend.
             return rcParams["backend"]
         else:
             return candidates
diff --git a/lib/matplotlib/tests/test_backend_qt4.py b/lib/matplotlib/tests/test_backend_qt4.py
@@ -13,10 +13,8 @@
 except ImportError:
     import mock
 
-with matplotlib.rc_context(rc={'backend': 'Qt4Agg'}):
-    qt_compat = pytest.importorskip('matplotlib.backends.qt_compat')
-from matplotlib.backends.backend_qt4 import (
-    MODIFIER_KEYS, SUPER, ALT, CTRL, SHIFT)  # noqa
+pytest.importorskip('PyQt4')
+qt_compat = pytest.importorskip('matplotlib.backends.qt_compat')
 
 QtCore = qt_compat.QtCore
 _, ControlModifier, ControlKey = MODIFIER_KEYS[CTRL]
diff --git a/lib/matplotlib/tests/test_backend_qt5.py b/lib/matplotlib/tests/test_backend_qt5.py
@@ -16,9 +16,10 @@
 except ImportError:
     import mock
 
-with matplotlib.rc_context(rc={'backend': 'Qt5Agg'}):
-    qt_compat = pytest.importorskip('matplotlib.backends.qt_compat',
-                                    minversion='5')
+pytest.importorskip('PyQt5')
+qt_compat = pytest.importorskip('matplotlib.backends.qt_compat',
+                                minversion='5')
+
 from matplotlib.backends.backend_qt5 import (
     MODIFIER_KEYS, SUPER, ALT, CTRL, SHIFT)  # noqa
 
