Avoid UnboundLocalError in drag_pan.

anntzer · anntzer · commit 78198bebd568 · 2018-02-16T11:04:52.000+01:00
Axes.drag_pan should probably have been private but it's public and
should therefore properly handle unexpected input.
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -4014,7 +4014,7 @@ def format_deltas(key, dx, dy):
         p = self._pan_start
         dx = x - p.x
         dy = y - p.y
-        if dx == 0 and dy == 0:
+        if dx == dy == 0:
             return
         if button == 1:
             dx, dy = format_deltas(key, dx, dy)
@@ -4035,6 +4035,8 @@ def format_deltas(key, dx, dy):
             except OverflowError:
                 warnings.warn('Overflow while panning')
                 return
+        else:
+            return
 
         valid = np.isfinite(result.transformed(p.trans))
         points = result.get_points().astype(object)
