Python ArgParse Subparsers and linking to the correct function

I'm creating a small Python script to manage different classes of servers (FTP, HTTP, SSH, etc.)

On each type of server, we can perform different types of actions (deploy, configure, check, etc.)

I have a base Server class, then a separate class for each type of server that inherits from this:

class Server:
    ...
    def check():
        ...

class HTTPServer(Server):
    def check():
        super(HTTPServer, self).check()
        ...
class FTPServer(Server):
    def check():
        super(FTPServer, self).check()
        ...

A sample command line might be:

my_program deploy http

From the command-line, the two mandatory arguments I need are:

1. Operation to perform
2. Type of server to create/manage

Previously, I was using argparse and the store operation, and using a dict to match the command-line option to the actual class and function name. For example:

types_of_servers = {
    'http': 'HTTPServer',
    'ftp': 'FTPServer',
    ...
}

valid_operations = {
    'check': 'check',
    'build': 'build',
    'deploy': 'deploy',
    'configure': 'configure',
    'verify': 'verify',
}

(In my actual code, valid_operations wasn't quite a naive 1:1 mapping.)

And then using rather horrible code to create the right type of object, and call the right class.

Then I thought I'd use argparse's subparsers feature to do it instead. So I've made each operation (check, build, deploy, etc.) a subparser.

Normally, I开发者_如何转开发 could link each sub-command to a particular function, and have it call it. However, I don't want to just call a generic check() function - I need to create the correct type of object first, and then call the appropriate function within that object.

Is there a good, or pythonic way to do this? Preferably one that doesn't involve a lot of hardcoding, or badly designed if/else loops?

If you are set on using a subparser for each command I would do something like this. Use argparse's type support to call a function that lookups the class you want to instantiate and returns it.

Then call the method on that instance dynamically with getattr()

import argparse

class Server:
    def check(self):
        return self.__class__.__name__

class FooServer(Server):
    pass

class BarServer(Server):
    pass


def get_server(server):
    try:
        klass = globals()[server.capitalize()+'Server']
        if not issubclass(klass, Server):
            raise KeyError

        return klass()
    except KeyError:
        raise argparse.ArgumentTypeError("%s is not a valid server." % server)


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    subparsers = parser.add_subparsers(dest='command')

    check = subparsers.add_parser('check')
    check.add_argument('server', type=get_server)

    args = parser.parse_args()

    print getattr(args.server, args.command)()

Output looks something like this:

$ python ./a.py check foo
FooServer
$ python ./a.py check bar
BarServer
$ python ./a.py check baz
usage: a.py check [-h] server
a.py check: error: argument server: baz is not a valid server.

You could just use the objects themselves in the dict.

#!/usr/bin/python

class Server:
    def __init__(self):
        pass

    def identify(self):
        print self.__class__.__name__

    def check(self):
        raise SomeErrorBecauseThisIsAbstract

class HttpServer(Server):

    def check(self, args):
        if self.verify_http_things():
           return True
        else:
           raise SomeErrorBecauseTheCheckFailed
    pass

class FtpServer(Server):

    def check(self, args):
        if self.verify_ftp_things():
           return True
        else:
           raise SomeErrorBecauseTheCheckFailed
    pass     


if __name__ == '__main__':


    # Hopefully this edit will make my intent clear:

    import argparse
    parser = argparse.ArgumentParser(description='Process some server commands')
    parser.add_argument('-c', dest='command')
    parser.add_argument('-t', dest='server_type')
    args = parser.parse_args()

    servers = {
        'http': HttpServer,
        'ftp': FtpServer
    }

    try:
        o = servers[args.server_type]()
        o.__call__(args.command)
    except Exception, e:
        print e

This should work (but a manual mapping would be more straight forward in my opinion):

import argparse

class Proxy:
    def __getattr__(thing):
        def caller (type):
            if type:
                server_object = # get instance of server with right type
                return getattr(server_object, thing)()
        return caller

parser = argparse.ArgumentParser()

entry_parser.add_argument('--server_type', dest='server_type', required=True,choices=['http', 'ftp', 'ssh'],)

subparser = parser.add_subparsers(dest='operation')
for operation in ['check', 'build', 'deploy', 'configure', 'verify']:
    entry_parser = subparser.add_parser(operation)
    entry_parser.set_defaults(func=getattr(Proxy, command))

options = parser.parse_args()

# this will call proxy function caller with type argument
options.func(options.server_type)