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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 get_network(self):
 """ Get the network that this resource attribute is in. """

        ref_key = self.ref_key
        if ref_key == 'NETWORK':
            return self.network
        elif ref_key == 'NODE':
            return self.node.network
        elif ref_key == 'LINK':
            return self.link.network
        elif ref_key == 'GROUP':
            return self.group.network
        elif ref_key == 'PROJECT':
            return None