On Sat, 21 Feb 2015 04:15:50 -0800, pfranken85 wrote: > Hello! > > I have a best-practice question: Imagine I have several hardware devices > that I work with on the same I2C bus and I am using the python smbus > module for that purpose. The individual devices are sensors, ADC, DAC > components. As I said, I would like to derive the corresponding classes > from one common class, let's say I2CDevice, so that they can share the > same bus connection (I don't want to do a import smbus, ..., self.bus = > smbus.SMBus(1) all the time). Of course, I could just pass the the bus > reference to each instance, but I am pretty sure that there must be a > nicer way to do this. > > In particular, I imagine the following: It should be possible that I > have two classes, ADC_I2C, DAC_I2C which share the same base class. Once > I create an instance of ADC_I2C or DAC_I2C it should check whether a bus > object exists, if not, it should create one and the other class should > be able to use this bus reference as well. Do you get my point? I am > pretty sure that such a design pattern should exist, maybe also in the > reference of DB connections? Unfortunately I did not find something like > this. > > Any hints are highly appreciated! > > Thanks!
So my experience doing similar work is with VMEBus, but if I were trying to do what you're doing, I'd take advantage of the fact that hardware isn't nearly as abstract as software. SMBus(1) represents three physical contiguous pieces of copper on a PCB somewhere. So I'd solve it with module level global variables. It's semi-frowned upon on software stuff because it creates an unintentional shared state between different modules, but you really HAVE a shared state, so it needs to be dealt with. So I'd put your ADC and DAC in the same package, whether all in one file or all in a package folder, and I'd give that package a: def getSMBus(busnumber): that takes care of the management of only creating each bus once. Then I'd give each class a: def __init__(busnumber): self.bus = getSMBus(busnumber) You could commonize that by deriving both classes from a common ancestor (all my VME modules derive from a common Region), but with only one piece of shared code between I don't think I'd bother. If you did, you could make the getSMBus code a classmethod just to make clear the lack of dependency on individual instances, but that starts to be code for code's sake. -- Rob Gaddi, Highland Technology -- www.highlandtechnology.com Email address domain is currently out of order. See above to fix. -- https://mail.python.org/mailman/listinfo/python-list
