return a shallow copy instead of deep copy

Author: margaret

pandas/core/indexing.py

@@ -1250,7 +1250,7 @@ def _get_slice_axis(self, slice_obj, axis=0):
         obj = self.obj
 
         if not need_slice(slice_obj):
-            return obj.copy()
+            return obj.copy(deep=False)
         indexer = self._convert_slice_indexer(slice_obj, axis)
 
         if isinstance(indexer, slice):
@@ -1349,7 +1349,7 @@ def _get_slice_axis(self, slice_obj, axis=0):
         """ this is pretty simple as we just have to deal with labels """
         obj = self.obj
         if not need_slice(slice_obj):
-            return obj.copy()
+            return obj.copy(deep=False)
 
         labels = obj._get_axis(axis)
         indexer = labels.slice_indexer(slice_obj.start, slice_obj.stop,
@@ -1690,7 +1690,7 @@ def _get_slice_axis(self, slice_obj, axis=0):
         obj = self.obj
 
         if not need_slice(slice_obj):
-            return obj.copy()
+            return obj.copy(deep=False)
 
         slice_obj = self._convert_slice_indexer(slice_obj, axis)
         if isinstance(slice_obj, slice):

pandas/tests/indexing/test_iloc.py

@@ -594,5 +594,9 @@ def test_iloc_empty_list_indexer_is_ok(self):
 
     def test_loc_identity_slice_returns_new_object(self):
         # GH13873
-        df = DataFrame({'a': [1, 3, 5], 'b': [2, 4, 6]})
-        assert not df.iloc[:] is df
+        df = DataFrame({'a': [1, 2, 3]})
+        result = df.iloc[:]
+        assert not result is df
+        # should be a shallow copy
+        df['a'] = [4, 4, 4]
+        assert (result['a'] == 4).all()

pandas/tests/indexing/test_loc.py

@@ -633,5 +633,9 @@ def test_loc_empty_list_indexer_is_ok(self):
 
     def test_loc_identity_slice_returns_new_object(self):
         # GH13873
-        df = DataFrame({'a': [1, 3, 5], 'b': [2, 4, 6]})
-        assert not df.loc[:] is df
+        df = DataFrame({'a': [1, 2, 3]})
+        result = df.loc[:]
+        assert not result is df
+        # should be a shallow copy
+        df['a'] = [4, 4, 4]
+        assert (result['a'] == 4).all()