Fix: Handle inline backends in plt_show (#14076)

Author: mh105

doc/changes/dev/14076.bugfix.rst

@@ -0,0 +1 @@
+Fix figures not being displayed in notebook-style frontends when using a Matplotlib inline backend, by `Mingjian He`_.

mne/viz/tests/test_utils.py

@@ -30,6 +30,7 @@
     centers_to_edges,
     compare_fiff,
     concatenate_images,
+    plt_show,
 )
 
 base_dir = Path(__file__).parents[2] / "io" / "tests" / "data"
@@ -46,6 +47,24 @@ def test_setup_vmin_vmax_warns():
         _setup_vmin_vmax(data=[-1, 0], vmin=None, vmax=None, norm=True)
 
 
+@pytest.mark.parametrize(
+    ("backend", "expected"),
+    (("module://Matplotlib_Inline.backend_inline", "pyplot"), ("QtAgg", "figure")),
+)
+def test_plt_show_backend(monkeypatch, backend, expected):
+    """Test backend-specific show paths."""
+    calls = []
+
+    class Figure:
+        def show(self, **kwargs):
+            calls.append(("figure", kwargs))
+
+    monkeypatch.setattr("matplotlib.get_backend", lambda: backend)
+    monkeypatch.setattr(plt, "show", lambda **kwargs: calls.append(("pyplot", kwargs)))
+    plt_show(fig=Figure(), block=True)
+    assert calls == [(expected, {"block": True})]
+
+
 def test_get_color_list():
     """Test getting a colormap from rcParams."""
     with rc_context({"axes.prop_cycle": cycler(color=["#ff0000", "#00ff00"])}):

mne/viz/utils.py

@@ -157,7 +157,12 @@ def plt_show(show=True, fig=None, **kwargs):
         backend = get_backend()
     if show and backend != "agg":
         logger.debug(f"Showing plot for backend {repr(backend)}")
-        (fig or plt).show(**kwargs)
+        # if backend is inline and therefore non-interactive,
+        # fig.show() fails with UserWarning. See gh-14076
+        if "inline" in str(backend).lower():
+            plt.show(**kwargs)
+        else:
+            (fig or plt).show(**kwargs)
 
 
 def _show_browser(show=True, block=True, fig=None, **kwargs):