Fix bug where list like object not returning empty Index.

pandas/core/frame.py

@@ -3402,7 +3402,7 @@ def _ensure_valid_index(self, value):
         passed value.
         """
         # GH5632, make sure that we are a Series convertible
-        if not len(self.index) and is_list_like(value):
+        if not len(self.index) and is_list_like(value) and len(value):
             try:
                 value = Series(value)
             except (ValueError, NotImplementedError, TypeError):

pandas/tests/indexing/test_indexing.py

@@ -717,6 +717,13 @@ def test_index_type_coercion(self):
                     idxr(s2)['0'] = 0
                     assert s2.index.is_object()
 
+    def test_empty_index_for_empty_dataframe(self):
+        index = pd.Index([], name='idx')
+        result = pd.DataFrame(columns=['A'], index=index)
+        result['A'] = []
+        expected = pd.DataFrame(columns=['A'], index=index)
+        tm.assert_index_equal(result.index, expected.index)
+
 
 class TestMisc(Base):
 

pandas/tests/indexing/test_partial.py

@@ -451,10 +451,10 @@ def test_partial_set_empty_frame(self):
         # these work as they don't really change
         # anything but the index
         # GH5632
-        expected = DataFrame(columns=['foo'], index=Index([], dtype='int64'))
+        expected = DataFrame(columns=['foo'], index=Index([], dtype='object'))
 
         def f():
-            df = DataFrame()
+            df = DataFrame(index=Index([], dtype='object'))
             df['foo'] = Series([], dtype='object')
             return df
 
@@ -478,22 +478,21 @@ def f():
         expected['foo'] = expected['foo'].astype('float64')
 
         def f():
-            df = DataFrame()
+            df = DataFrame(index=Index([], dtype='int64'))
             df['foo'] = []
             return df
 
         tm.assert_frame_equal(f(), expected)
 
         def f():
-            df = DataFrame()
+            df = DataFrame(index=Index([], dtype='int64'))
             df['foo'] = Series(np.arange(len(df)), dtype='float64')
             return df
 
         tm.assert_frame_equal(f(), expected)
 
         def f():
-            df = DataFrame()
-            tm.assert_index_equal(df.index, Index([], dtype='object'))
+            df = DataFrame(index=Index([], dtype='int64'))
             df['foo'] = range(len(df))
             return df