Invert code to in datatype validation

pandas/core/frame.py

@@ -2475,20 +2475,20 @@ def _ensure_valid_index(self, value):
         """
         # GH5632, make sure that we are a Series convertible
         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:
+            if not is_list_like(value):
                 # GH16823, Raise an error due to loss of information
                 raise ValueError('If using all scalar values, you must pass'
                                  ' an index')
+            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)
+
 
     def _set_item(self, key, value):
         """