Dynamic importing of modules followed by instantiation of objects with a certain baseclass from said modules

Question

I\'m writing an application. No fancy GUI:s or anything, just a plain old console application. This application, lets call it App, needs to be able to load plugins on startu

Answer 1

Here is a meta-classier way to register the plugins:

Define PluginBase to be of type PluginType. PluginType automatically registers any instance (class) in the plugins set.

plugin.py:

plugins=set()
class PluginType(type):
    def __init__(cls, name, bases, attrs):
        super(PluginType, cls).__init__(name, bases, attrs)
        # print(cls, name,cls.__module__)
        plugins.add(cls)

class PluginBase(object):
    __metaclass__=PluginType
    pass

This is the part that the user writes. Notice that there is nothing special here.

pluginDir/myplugin.py:

import plugin
class Foo(plugin.PluginBase):
    pass

Here is what the search function might look like:

test.py:

import plugin
import os
import imp

def search(plugindir):
    for root, dirs, files in os.walk(plugindir):
        for fname in files:
            modname = os.path.splitext(fname)[0]
            try:
                module=imp.load_source(modname,os.path.join(root,fname))
            except Exception: continue

search('pluginDir')
print(plugin.plugins)

Running test.py yields

set([])