Choose adapter dynamically depending on librarie(s) installed

Question

I am designing a library that has adapters that supports a wide-range of libraries. I want the library to dynamically choose which ever adapter that has the library it uses

Answer 1

You've got the right idea. Your case works because each subobject has the same sort of classes e.g. both APIs have a class called Publisher and you can just make sure the correct version is imported.

If this isn't true (if possible implementation A and B are not similar) you write your own facade, which is just your own simple API that then calls the real API with the correct methods/parameters for that library.

Obviously switching between choices may require some overhead (i don't know your case, but for instance, let's say you had two libraries to walk through an open file, and the library handles opening the file. You can't just switch to the second library in the middle of the file and expect it to start where the first library stopped). But it's just a matter of saving it:

accessmethods = {}
try:
    from modA.modB import classX as apiA_classX
    from modA.modB import classY as apiA_classY
    accessmethods['apiA'] = [apiA_classX, apiA_classY]
    classX = apiA_classX
    classY = apiA_classY
except:
    pass

try:
    from modC.modD import classX as apiB_classX
    from modC.modD import classY as apiB_classY
    accessmethods['apiB'] = [apiB_classX, apiB_classY]
    classX = apiB_classX
    classY = apiB_classY
except:
    pass

def switchMethod(method):
    global classX
    global classY
    try: 
        classX, classY = accessmethods[method]
    except KeyError as e:
        raise ValueError, 'Method %s not currently available'%method

etc.