Fix valinit argument to RangeSlider

Author: dstansby

lib/matplotlib/tests/test_widgets.py

@@ -308,10 +308,14 @@ def test_range_slider(orientation):
     fig, ax = plt.subplots()
 
     slider = widgets.RangeSlider(
-        ax=ax, label="", valmin=0.0, valmax=1.0, orientation=orientation
+        ax=ax, label="", valmin=0.0, valmax=1.0, orientation=orientation,
+        valinit=[0.1, 0.34]
     )
     box = slider.poly.get_extents().transformed(ax.transAxes.inverted())
-    assert_allclose(box.get_points().flatten()[idx], [0.25, 0, 0.75, 1])
+    assert_allclose(box.get_points().flatten()[idx], [0.1, 0, 0.34, 1])
+
+    # Check initial value is set correctly
+    assert_allclose(slider.val, (0.1, 0.34))
 
     slider.set_val((0.2, 0.6))
     assert_allclose(slider.val, (0.2, 0.6))

lib/matplotlib/widgets.py

@@ -608,12 +608,13 @@ def __init__(
         super().__init__(ax, orientation, closedmin, closedmax,
                          valmin, valmax, valfmt, dragging, valstep)
 
+        # Set a value to allow _value_in_bounds() to work.
+        self.val = [valmin, valmax]
         if valinit is None:
             # Place at the 25th and 75th percentiles
             extent = valmax - valmin
-            valinit = np.array(
-                [valmin + extent * 0.25, valmin + extent * 0.75]
-            )
+            valinit = np.array([valmin + extent * 0.25,
+                                valmin + extent * 0.75])
         else:
             valinit = self._value_in_bounds(valinit)
         self.val = valinit
@@ -684,8 +685,9 @@ def _max_in_bounds(self, max):
             max = self.val[0]
         return self._stepped_value(max)
 
-    def _value_in_bounds(self, val):
-        return (self._min_in_bounds(val[0]), self._max_in_bounds(val[1]))
+    def _value_in_bounds(self, vals):
+        """Clip min, max values to the bounds."""
+        return (self._min_in_bounds(vals[0]), self._max_in_bounds(vals[1]))
 
     def _update_val_from_pos(self, pos):
         """Update the slider value based on a given position."""