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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def call(self, rs, name, user, fields):
 """Invoke a previously loaded object. :param RiveScript rs: the parent RiveScript instance. :param str name: The name of the object macro to be called. :param str user: The user ID invoking the object macro. :param []str fields: Array of words sent as the object's arguments. :return str: The output of the object macro. """

        # Call the dynamic method.
        if name not in self._objects:
            return '[ERR: Object Not Found]'
        func = self._objects[name]
        reply = ''
        try:
            reply = func(rs, fields)
            if reply is None:
                reply = ''
        except Exception as e:
            raise PythonObjectError("Error executing Python object: " + str(e))
        return text_type(reply)