subnet_stuff.py

def _manage_igw(self):
    """This works fine"""
    name = f'{self.name}-igw'
    print(f'VPC ID before ec2.InternetGateway: {self.vpc.id}')
    ec2.InternetGateway(name,
                        tags=merge_tags_with_name(name, self._options.tags),
                        vpc_id=self.vpc.id)

def _manage_natgw(self):
    """This raises an exception on `get_subnet_ids`"""
    name = f'{self.name}-natgw'
    print(f'VPC ID before deriving subnets for ec2.NatGateway: {self.vpc.id}')

    subnets = ec2.get_subnet_ids(vpc_id=self.vpc.id)