On Fri, 21 Feb 2014 12:59:11 -0800, Denis Usanov wrote: > I mostly develop on Python some automation scripts such as deployment > (it's not about fabric and may be not ssh at all), testing something, > etc. In this terms I have such abstraction as "step". > > Some code: > > class IStep(object): > def run(): > raise NotImplementedError() > > And the certain steps: > > class DeployStep: ... > class ValidateUSBFlash: ... > class SwitchVersionS: ... > > Where I implement run method.
Why are these classes? Unless you have multiple instances, or are using inheritance, the use of classes is a Java-ism and a waste of time. http://steve-yegge.blogspot.com/2006/03/execution-in-kingdom-of-nouns.html Since I see no reason to (say) have multiple ValidateUSBFlash instances, with different state, at the same time, and no reason to have (say) SwitchVersionS inherit from (say) DeployStep, I suggest a better approach is to use functions. No more ValidateUSBFlash.run method calls, just call function validate_usb_flash. > Then I use some "builder" class which can add steps to internal list and > has a method "start" running all step one by one. That becomes: steps = [deploy_step, validate_usb_flash, switch_version_s, ...] for step in steps: step() > And I like this. It's loosely coupled system. It works fine in simple > cases. But sometimes some steps have to use the results from previous > steps. And now I have problems. Before now I had internal dict in > "builder" and named it as "world" and passed it to each run() methods of > steps. It worked but I disliked this. > > How would you solve this problem and how would you do it? I understant > that it's more architecture specific question, not a python one. I'd avoid over-generalisation, and just write a script. Let each step function take whatever arguments it needs, and return whatever arguments it requires, then write it like this: deploy_step() result = validate_usb_flash() if result == 1: validate_other_usb_flash() else: validate_something_else(result) I mean, how many steps do you have? Twenty? A hundred? It's not that hard to maintain a 100 or 200 line script. And are you likely to have so many different versions of it that you need extra abstraction layers? Of course, I might be misinterpreting your post. Perhaps you do have so many steps, and so many different types of deployment, that you do need a more heavily abstracted system. In that case, I think you need to describe your system in more detail to get any useful answers. But don't over-generalise, and don't become an Architecture Astronaut :-) -- Steven -- https://mail.python.org/mailman/listinfo/python-list
