code: def ec2_vpc_subnets(self, lookup, default=None):
      
      vpc_id = self.ec2_vpc_vpc_id(lookup)
      if vpc_id is None:
        return default
      subnets = EFAwsResolver.__CLIENTS["ec2"].describe_subnets(Filters=[{
        'Name': 'vpc-id',
        'Values': [vpc_id]
      }])
      if len(subnets["Subnets"]) > 0:
        # Strip the metadata section (subnets["Subnets"])
        subnet_list = [s["SubnetId"] for s in subnets["Subnets"]]
        # Add internal ", " only. This is called literally from: "{{aws...}}" - reuses the outer quotes
        return "\", \"".join(subnet_list)
      else:
        return default
docs: Args:
        lookup - the friendly name of the VPC whose subnets we want
      Returns:
        A comma-separated list of all subnets in use in the named VPC or default/None if no match found