code: def get_subnet_dict():
    
    subnet_dict = {}
    vpc = get_vpc()
    for subnet in vpc.subnets.all():
      zone = subnet.availability_zone
      assert zone not in subnet_dict, "More than one subnet in %s, why?" % (zone,)
      subnet_dict[zone] = subnet
    return subnet_dict
docs: Returns dictionary of "availability zone" -> subnet for current VPC.