code: def ec2_vpc_availabilityzones(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"])
        az_list = [s["AvailabilityZone"] for s in subnets["Subnets"]]
        # Add internal ", " only. This is called literally from: "{{aws...}}" - CF template needs the outer quotes
        return "\", \"".join(az_list)
      else:
        return default
docs: Args:
        lookup: the friendly name of a VPC to look up
        default: the optional value to return if lookup failed; returns None if not set
      Returns:
        A comma-separated list of availability zones in use in the named VPC or default/None if no match