refactor

holoviews/core/data/ibis.py

@@ -111,13 +111,14 @@ def nonzero(cls, dataset):
     @cached
     def range(cls, dataset, dimension):
         dimension = dataset.get_dimension(dimension, strict=True)
-        if cls.dtype(dataset, dimension).kind == 'O':
+        dtype_kind = cls.dtype(dataset, dimension).kind
+        if dtype_kind == 'O':
             # Can this be done more efficiently?
             column = dataset.data[dimension.name].execute()
             first = column.iloc[0]
             last = column.iloc[-1]
             return first, last
-        if cls.dtype(dataset, dimension).kind in 'SU':
+        if dtype_kind in 'SU':
             return None, None
         if dimension.nodata is not None:
             return Interface.range(dataset, dimension)