Raise ValueError when setting scalars in a df with no index

Author: alanbato

pandas/core/frame.py

@@ -2474,16 +2474,21 @@ 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):
-            try:
-                value = Series(value)
-            except:
-                raise ValueError('Cannot set a frame with no defined index '
-                                 'and a value that cannot be converted to a '
-                                 'Series')
-
-            self._data = self._data.reindex_axis(value.index.copy(), axis=1,
-                                                 fill_value=np.nan)
+        if not len(self.index):
+            if is_list_like(value):
+                try:
+                    value = Series(value)
+                except:
+                    raise ValueError('Cannot set a frame with no defined'
+                                     'index and a value that cannot be '
+                                     'converted to a Series')
+
+                self._data = self._data.reindex_axis(value.index.copy(), axis=1,
+                                                     fill_value=np.nan)
+            else:
+                # GH16823, Raise an error due to loss of information
+                raise ValueError('If using all scalar values, you must pass'
+                                 ' an index')
 
     def _set_item(self, key, value):
         """