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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 set_if_unset(self, key, value):
 """Set a particular spark property by the string key name if it hasn't already been set. This method allows chaining so that i can provide a similar feel to the standard Scala way of setting multiple configurations Parameters key : string value : string Returns ------- self """

        if key not in self._conf_dict:
            self.set(key, value)
        return self