Class factory in Python

Question

I\'m new to Python and need some advice implementing the scenario below.

I have two classes for managing domains at two different registrars. Both have the same inte

Answer 1

I have this problem all the time. If you have the classes embedded in your application (and its modules) then you can use a function; but if you load plugins dynamically, you need something more dynamic -- registering the classes with a factory via metaclasses automatically.

Here is a pattern I'm sure I lifted from StackOverflow originally, but I don't still have the path to the original post

_registry = {}

class PluginType(type):
    def __init__(cls, name, bases, attrs):
        _registry[name] = cls
        return super(PluginType, cls).__init__(name, bases, attrs)

class Plugin(object):
    __metaclass__  = PluginType # python <3.0 only 
    def __init__(self, *args):
        pass

def load_class(plugin_name, plugin_dir):
    plugin_file = plugin_name + ".py"
    for root, dirs, files in os.walk(plugin_dir) :
        if plugin_file in (s for s in files if s.endswith('.py')) :
            fp, pathname, description = imp.find_module(plugin_name, [root])
            try:
                mod = imp.load_module(plugin_name, fp, pathname, description)
            finally:
                if fp:
                    fp.close()
    return

def get_class(plugin_name) :
    t = None
    if plugin_name in _registry:
        t = _registry[plugin_name]
    return t

def get_instance(plugin_name, *args):
    return get_class(plugin_name)(*args)