Question

We have a simple Python program to manage various types of in-house servers, using argparse:

manage_servers.py <operation> <type_of_server> 

Operations are things like check, build, deploy, configure, verify etc.

Types of server are just different types of inhouse servers we use.

We have a generic server class, then specific types that inherit from that:

class Server
    def configure_logging(self, loggin_file):
        ...
    def check(self):
        ...
    def deploy(self):
        ...
    def configure(self):
        ...
    def __init__(self, hostname):
        self.hostname = hostname
        logging = self.configure_logging(LOG_FILENAME)
class SpamServer(Server):
    def check(self):
        ...
class HamServer(Server):
    def deploy(self):
        ...

My question is how to link that all up to argparse?

Originally, I was using argparse subparses for the operations (check, build, deploy) and another argument for the type.

subparsers = parser.add_subparsers(help='The operation that you want to run on the server.')
parser_check = subparsers.add_parser('check', help='Check that the server has been setup correctly.')
parser_build = subparsers.add_parser('build', help='Download and build a copy of the execution stack.')
parser_build.add_argument('-r', '--revision', help='SVN revision to build from.')
...
parser.add_argument('type_of_server', action='store', choices=types_of_servers,
                    help='The type of server you wish to create.')

Normally, you’d link each subparse to a method – and then pass in the type_of_server as an argument. However, that’s slightly backwards due to the classes- I need to create an instance of the appropriate Server class, then call the operation method inside of that.

Any ideas of how I could achieve the above? Perhaps a different design pattern for Servers? Or a way to still use argparse as is?

Cheers,
Victor

Answer 1

Just use the parser.add_subparsers(dest=... argument with a mapping of type_of_server to classes:

subparsers = parser.add_subparsers(dest='operation', help='The operation that you want to run on the server.')
...
server_types = dict(spam=SpamServer, ham=HamServer)
args = parser.parse_args()
server = server_types[args.type_of_server]()
getattr(server, args.operation)(args)