<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_pass_thru(pass_thrus):
 """ Decorator adds explicit pass-through visit and depart methods """

    def meth(self, node):
        pass

    def dec(cls):
        for element_name in pass_thrus:
            for meth_prefix in ('visit_', 'depart_'):
                meth_name = meth_prefix + element_name
                if hasattr(cls, meth_name):
                    raise ValueError('method name {} already defined'
                                     .format(meth_name))
                setattr(cls, meth_name, meth)
        return cls

    return dec