dates: add warning for usec precision with high years

nmartensen · nmartensen · commit a5cddc086cb9 · 2017-12-23T19:41:39.000+01:00
diff --git a/lib/matplotlib/dates.py b/lib/matplotlib/dates.py
@@ -1304,6 +1304,10 @@ def get_locator(self, dmin, dmax):
             locator = RRuleLocator(rrule, self.tz)
         else:
             locator = MicrosecondLocator(interval, tz=self.tz)
+            if dmin.year > 20:
+                warnings.warn('The MicrosecondLocator needs very early years'
+                        'to work really well. Please see the '
+                        'documentation for details.')
 
         locator.set_axis(self.axis)
 
