swev-id: matplotlib__matplotlib-23299 Preserve figures when resolving auto backend

lib/matplotlib/__init__.py

@@ -674,7 +674,12 @@ def __getitem__(self, key):
             val = dict.__getitem__(self, key)
             if val is rcsetup._auto_backend_sentinel:
                 from matplotlib import pyplot as plt
+                if plt._backend_mod is not None:
+                    import matplotlib.backends
+                    return matplotlib.backends.backend
                 plt.switch_backend(rcsetup._auto_backend_sentinel)
+                return dict.__getitem__(self, key)
+            return val
 
         return dict.__getitem__(self, key)
 

lib/matplotlib/tests/test_backends_interactive.py

@@ -270,6 +270,33 @@ def test_lazy_auto_backend_selection():
                 timeout=_test_timeout)
 
 
+def _impl_get_backend_preserves_figures():
+    import matplotlib
+    from matplotlib import get_backend, rc_context, rcsetup
+    from matplotlib import pyplot as plt
+
+    plt.close("all")
+    matplotlib.rcParams["backend"] = rcsetup._auto_backend_sentinel
+
+    with rc_context():
+        plt.figure()
+
+    matplotlib.rcParams["backend"] = rcsetup._auto_backend_sentinel
+    assert plt._backend_mod is not None
+
+    gcf = plt._pylab_helpers.Gcf
+    assert tuple(gcf.figs.items())
+    before = (id(gcf), tuple(gcf.figs.items()))
+    get_backend()
+    after = (id(gcf), tuple(gcf.figs.items()))
+    assert before == after
+
+
+def test_get_backend_preserves_figures():
+    _run_helper(_impl_get_backend_preserves_figures,
+                timeout=_test_timeout)
+
+
 def _implqt5agg():
     import matplotlib.backends.backend_qt5agg  # noqa
     import sys