Pass axis parameter of DataFrame.diff through _get_block_manager_axis

Author: evanpw

pandas/core/frame.py

@@ -3597,10 +3597,8 @@ def diff(self, periods=1, axis=0):
         -------
         diffed : DataFrame
         """
-        # Invert the axis to match the convention of np.diff
-        axis = 1 - self._get_axis_number(axis)
-
-        new_data = self._data.diff(n=periods, axis=axis)
+        bm_axis = self._get_block_manager_axis(axis)
+        new_data = self._data.diff(n=periods, axis=bm_axis)
         return self._constructor(new_data)
 
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