suggestion: Name it what it is, then there's never any confusion. So:

    conts_obj = DockerContainers(self.parent_subtest)
    self.sub_stuff["conts_obj"] = conts_obj

or


    dc = DockerContainers(self.parent_subtest)
    self.sub_stuff["dc"] = dc

or 

    dc = self.sub_stuff["dc"] = DockerContainers(self.parent_subtest)

Just makes it easier for old/tired eyes to reference when we can't remember what something was defined as :grinning: