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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_in_net_id(cls, tenant_id):
 """Retrieve the network ID of IN network. """

        if 'in' not in cls.ip_db_obj:
            LOG.error("Fabric not prepared for tenant %s", tenant_id)
            return None
        db_obj = cls.ip_db_obj.get('in')
        in_subnet_dict = cls.get_in_ip_addr(tenant_id)
        sub = db_obj.get_subnet(in_subnet_dict.get('subnet'))
        return sub.network_id