silence import warning (#2635)

Author: max-sixty

xarray/core/indexing.py

@@ -2,7 +2,7 @@
 
 import functools
 import operator
-from collections import Hashable, defaultdict
+from collections import defaultdict
 from datetime import timedelta
 
 import numpy as np
@@ -13,6 +13,11 @@
     dask_array_type, integer_types, iteritems, range, suppress)
 from .utils import is_dict_like
 
+try:
+    from collections.abc import Hashable
+except ImportError:  # Py2
+    from collections import Hashable
+
 
 def expanded_indexer(key, ndim):
     """Given a key for indexing an ndarray, return an equivalent key which is a