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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 exists(self, key, fresh=False):
 """Check if key exists :param key: the name of setting variable :param fresh: if key should be taken from source direclty :return: Boolean """

        key = key.upper()
        if key in self._deleted:
            return False
        return self.get(key, fresh=fresh, default=missing) is not missing