allow not drawing the line marking initial slider position

ianhi · ianhi · commit caa3f426647f · 2020-10-31T20:14:44.000-04:00
diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
@@ -255,7 +255,7 @@ class Slider(AxesWidget):
     def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt=None,
                  closedmin=True, closedmax=True, slidermin=None,
                  slidermax=None, dragging=True, valstep=None,
-                 orientation='horizontal', **kwargs):
+                 orientation='horizontal', *, initcolor='r', **kwargs):
         """
         Parameters
         ----------
@@ -295,13 +295,17 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt=None,
         dragging : bool, default: True
             If True the slider can be dragged by the mouse.
 
-        valstep : float or arraylike, default: None
+        valstep : float or array-like, default: None
             If a float, the slider will snap to multiples of *valstep*.
             If an array the slider will snap to the values in the array.
 
         orientation : {'horizontal', 'vertical'}, default: 'horizontal'
             The orientation of the slider.
 
+        initcolor : color or None, default: 'r'
+            The color of the line at the *valinit* position. If None then
+            no line will be drawn.
+
         Notes
         -----
         Additional kwargs are passed on to ``self.poly`` which is the
@@ -338,10 +342,12 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt=None,
         self.valinit = valinit
         if orientation == 'vertical':
             self.poly = ax.axhspan(valmin, valinit, 0, 1, **kwargs)
-            self.hline = ax.axhline(valinit, 0, 1, color='r', lw=1)
+            if initcolor is not None:
+                self.hline = ax.axhline(valinit, 0, 1, color=initcolor, lw=1)
         else:
             self.poly = ax.axvspan(valmin, valinit, 0, 1, **kwargs)
-            self.vline = ax.axvline(valinit, 0, 1, color='r', lw=1)
+            if initcolor is not None:
+                self.vline = ax.axvline(valinit, 0, 1, color=initcolor, lw=1)
 
         if orientation == 'vertical':
             ax.set_ylim((valmin, valmax))
