fix transpose docstring. Closes pydata#2576

Author: dcherian

xarray/core/dataarray.py

@@ -1385,8 +1385,9 @@ def transpose(self, *dims):
 
         Notes
         -----
-        Although this operation returns a view of this array's data, it is
-        not lazy -- the data will be fully loaded.
+        This operation returns a view of this array's data. It is
+        lazy for dask-backed DataArrays but not for numpy-backed DataArrays
+        -- the data will be fully loaded.
 
         See Also
         --------

xarray/core/dataset.py

@@ -2817,8 +2817,9 @@ def transpose(self, *dims):
 
         Notes
         -----
-        Although this operation returns a view of each array's data, it
-        is not lazy -- the data will be fully loaded into memory.
+        This operation returns a view of each array's data. It is
+        lazy for dask-backed DataArrays but not for numpy-backed DataArrays
+        -- the data will be fully loaded into memory.
 
         See Also
         --------

xarray/core/variable.py

@@ -1133,8 +1133,8 @@ def transpose(self, *dims):
 
         Notes
         -----
-        Although this operation returns a view of this variable's data, it is
-        not lazy -- the data will be fully loaded.
+        This operation returns a view of this variable's data. It is
+        lazy for dask-backed Variables but not for numpy-backed Variables.
 
         See Also
         --------