INT/CLN: clean up block slicing semantics

Author: jreback

pandas/core/internals.py

@@ -2693,22 +2693,31 @@ def get_slice(self, slobj, axis=0, raise_on_error=False):
         return bm
 
     def _slice_blocks(self, slobj, axis):
-        new_blocks = []
+        """
+        slice the blocks using the provided slice object
+        this is only for slicing on axis != 0
+        """
+
+        if axis == 0:
+            raise AssertionError("cannot _slice_blocks on axis=0")
 
         slicer = [slice(None, None) for _ in range(self.ndim)]
         slicer[axis] = slobj
         slicer = tuple(slicer)
+        is_unique = self.axes[0].is_unique
 
-        for block in self.blocks:
-            newb = make_block(block._slice(slicer),
-                              block.items,
-                              block.ref_items,
-                              klass=block.__class__,
-                              fastpath=True,
-                              placement=block._ref_locs)
-            newb.set_ref_locs(block._ref_locs)
-            new_blocks.append(newb)
-        return new_blocks
+        def place(block):
+            if not is_unique:
+                return block._ref_locs
+            return None
+
+        return [ make_block(block._slice(slicer),
+                            block.items,
+                            block.ref_items,
+                            klass=block.__class__,
+                            fastpath=True,
+                            placement=place(block)
+                            ) for block in self.blocks ]
 
     def get_series_dict(self):
         # For DataFrame

pandas/tests/test_indexing.py

@@ -380,21 +380,19 @@ def test_iloc_exceeds_bounds(self):
         assert_series_equal(result,expected)
 
         # doc example
-        df = DataFrame(np.random.randn(5,2),columns=list('AB'))
-        self.assertRaises(IndexError, lambda : df.iloc[[4,5,6]])
-        self.assertRaises(IndexError, lambda : df.iloc[:,4])
+        def check(result,expected):
+            str(result)
+            result.dtypes
+            assert_frame_equal(result,expected)
 
-        result = df.iloc[4:6]
-        expected = df.iloc[[4]]
-        assert_frame_equal(result,expected)
+        dfl = DataFrame(np.random.randn(5,2),columns=list('AB'))
+        check(dfl.iloc[:,2:3],DataFrame(index=dfl.index))
+        check(dfl.iloc[:,1:3],dfl.iloc[:,[1]])
+        check(dfl.iloc[4:6],dfl.iloc[[4]])
 
-        result = df.iloc[:,2:3]
-        expected = DataFrame(index=df.index)
-        assert_frame_equal(result,expected)
+        self.assertRaises(IndexError, lambda : dfl.iloc[[4,5,6]])
+        self.assertRaises(IndexError, lambda : dfl.iloc[:,4])
 
-        result = df.iloc[:,1:3]
-        expected = df.iloc[:,[1]]
-        assert_frame_equal(result,expected)
 
     def test_iloc_getitem_int(self):