Allow to not draw the labels on pie chart.

Carreau · Carreau · commit 6e7bfefd87ae · 2018-08-02T10:05:08.000-07:00
for consistency with other API it is relatively easy and desirable to be
able to pass the `label` and call `legend()` after the fact; which will
display the legend in a box in one of the corner.

When doing so, having the label on each piece of pie does not make much
sens (and may clobber the pie chart). Thus allow to use ``None`` as a
value for ``labeldistance`` as a way to not draw them.
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -2735,8 +2735,10 @@ def pie(self, x, explode=None, labels=None, colors=None,
         shadow : bool, optional, default: False
             Draw a shadow beneath the pie.
 
-        labeldistance : float, optional, default: 1.1
-            The radial distance at which the pie labels are drawn
+        labeldistance : float or None, optional, default: 1.1
+            The radial distance at which the pie labels are drawn.
+            If set to ``None``, label are not drawn, but are stored for use in
+            ``legend()``
 
         startangle : float, optional, default: None
             If not *None*, rotates the start of the pie chart by *angle*
@@ -2858,23 +2860,24 @@ def get_next_color():
                 shad.set_label('_nolegend_')
                 self.add_patch(shad)
 
-            xt = x + labeldistance * radius * math.cos(thetam)
-            yt = y + labeldistance * radius * math.sin(thetam)
-            label_alignment_h = xt > 0 and 'left' or 'right'
-            label_alignment_v = 'center'
-            label_rotation = 'horizontal'
-            if rotatelabels:
-                label_alignment_v = yt > 0 and 'bottom' or 'top'
-                label_rotation = np.rad2deg(thetam) + (0 if xt > 0 else 180)
-            props = dict(horizontalalignment=label_alignment_h,
-                          verticalalignment=label_alignment_v,
-                          rotation=label_rotation,
-                          size=rcParams['xtick.labelsize'])
-            props.update(textprops)
-
-            t = self.text(xt, yt, label, **props)
-
-            texts.append(t)
+            if labeldistance is not None:
+                xt = x + labeldistance * radius * math.cos(thetam)
+                yt = y + labeldistance * radius * math.sin(thetam)
+                label_alignment_h = xt > 0 and 'left' or 'right'
+                label_alignment_v = 'center'
+                label_rotation = 'horizontal'
+                if rotatelabels:
+                    label_alignment_v = yt > 0 and 'bottom' or 'top'
+                    label_rotation = np.rad2deg(thetam) + (0 if xt > 0 else 180)
+                props = dict(horizontalalignment=label_alignment_h,
+                            verticalalignment=label_alignment_v,
+                            rotation=label_rotation,
+                            size=rcParams['xtick.labelsize'])
+                props.update(textprops)
+
+                t = self.text(xt, yt, label, **props)
+
+                texts.append(t)
 
             if autopct is not None:
                 xt = x + pctdistance * radius * math.cos(thetam)
