Don't bother with manually resizing the Qt main window.

anntzer · anntzer · commit e6367c9c4041 · 2019-07-05T19:02:04.000+02:00
The presence of FigureCanvasQT.sizeHint is sufficient to get a correct
figure size; Qt properly determines the entire window size based on
that.

This behavior is already tested by test_backend_qt::test_dpi_ratio_change,
and one can also manually check that the patch does not change physical
window sizes when creating figures of various figsize=(?).
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -571,16 +571,6 @@ def __init__(self, canvas, num):
                 statusbar_label = QtWidgets.QLabel()
                 self.window.statusBar().addWidget(statusbar_label)
                 self.toolbar.message.connect(statusbar_label.setText)
-            tbs_height = self.toolbar.sizeHint().height()
-        else:
-            tbs_height = 0
-
-        # resize the main window so it will display the canvas with the
-        # requested size:
-        cs = canvas.sizeHint()
-        sbs = self.window.statusBar().sizeHint()
-        height = cs.height() + tbs_height + sbs.height()
-        self.window.resize(cs.width(), height)
 
         self.window.setCentralWidget(self.canvas)
 
