BUG: fix for bug 16493

Author: CRP

pandas/io/formats/format.py

@@ -1292,9 +1292,9 @@ def _column_header():
             self.write_tr(col_row, indent, self.indent_delta, header=True,
                           align=align)
 
-        if all(self.fmt.has_index_names,
+        if all((self.fmt.has_index_names,
                 self.fmt.index,
-                self.fmt.show_index_names):
+                self.fmt.show_index_names)):
             row = ([x if x is not None else ''
                     for x in self.frame.index.names] +
                    [''] * min(len(self.columns), self.max_cols))