Merge pull request #273 from alpha-beta-soup/iss272

fix #272

Author: WeatherGod

lib/mpl_toolkits/basemap/__init__.py

@@ -4700,9 +4700,9 @@ def nightshade(self,date,color="k",delta=0.25,alpha=0.5,ax=None,zorder=2):
         returns a matplotlib.contour.ContourSet instance.
         """
         from .solar import daynight_grid
-        # make sure date is utc.
-        if date.utcoffset() is not None:
-            raise ValueError('datetime instance must be UTC')
+        # make sure date is UTC, or naive with repect to time zones
+        if date.utcoffset():
+            raise ValueError('datetime instance must be UTC, not {}'.format(date.tzname()))
         # create grid of day=0, night=1
         lons,lats,daynight = daynight_grid(date,delta,self.lonmin,self.lonmax)
         x,y = self(lons,lats)