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If it's in the same project, then you should try very hard not to have an workflow like this. Essentially you're trying to make something declarative appear to be imperative. It's just not designed this way.

Instead you should do your calculation unconditionally and apply results to the new and old subnets.

I want declarative, but compositionally declarative. So, in a VPC object I want to be able to say I want 3 public subnets, and 5 private subnets - and then I want that to be calculated. The issue is say I loop to create the subnet objects, and I do public then private - but later I add more public subnets it will break without some kind of awareness of what existed previously. If there isn't a pulumi native way to get state info I might try pickling the objects.

Later, you cannot add more public subnets. If you did that, then you'd need to manage the VPC in two projects, which is not to be recommended.

Instead, figure out how many subnets you need, and define them all at once.

Creating subnets in a loop is also something I don't recommend. That's how awsx.ec2.Vpc works, and it causes headaches for Pulumi newbies :disappointed:

You can work with multiple projects to create the subnets if you need to: so long as only one of them manages the VPC then you can use stack references or config to pass the VPC id to anywhere it's needed.

Hopefully there's a way to work around the multi-step subnet creation projects. For example, if I was creating a system with a single VPC, with a subnet per dynamically-created target environment, then I'd have one project for the VPC (and maybe the default subnets, admin access, etc.). And I'd have a separate project, with a stack per target environment, which grabs the VPC id from the first project, and creates the subnet using the id.

(Though in this case I'd recommend multiple VPCs :slightly_smiling_face: )

After fighting with it, I am accepting that pulumi is pythonic but not python and submitting myself to projects/stacks and stack references - so you were right.

```private_subnets = []
for subnet in range(1, number_of_azs + 1):
    ec2_subnet = aws.ec2.Subnet(
        f"{env}-ec2Subnet-{subnet}-{suffix}",
        availability_zone=available_azs.names[subnet - 1],
        cidr_block=f"10.27.{subnet}.0/24",
        vpc_id=vpc.id,
        map_public_ip_on_launch=False,
        tags={
            "Type": "Private",
            "Name": f"{env}-ec2Subnet-{subnet}-private-{suffix}",
        },
        opts=pulumi.ResourceOptions(provider=provider),
    )
    private_subnets.append(ec2_subnet)```
will this work? I need to get the subnet ids at the end..However I am still getting each element as type Output... So this wont work?

This works. You _cannot_ get the subnet id at this top code level though. You can _only_ get it inside an apply().