Broker should filter which objects it imports

[turicas]

Should not be needed to specify a __all__ in the workers module: Broker should inspect the module for classes that inherit from pypelinin.Worker.

[turicas]

Maybe (but probably not) we can use decorators instead of inheritance to specify that a class is a worker, but probably a better approach is to use inheritance since we can add helper methods to Worker.

[israelst]

We could use both solutions. Use inheritance and the decorator which we have done together.

def Worker(requires):
    def Worker2(worker_function):
        class WorkerClass(object):
            def process(self, document):
                document['passou'] = 'por aqui'
                return worker_function(document)
        WorkerClass.requires = requires
        return WorkerClass
    return Worker2

@Worker(requires=['teste'])
def Teste(document):
    return document