<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _add(self, symbol_name, namespace, node, module):
 """Helper function for adding symbols. See add_symbol(). """

        result = symbol_name in namespace
        namespace[symbol_name] = node, module
        return not result