python - 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 installed on the machine when importing specific classes.

The goal is to be able to change the library that the program depends on without having to make modifications to the code. This particular feature is for handling RabbitMQ connections, as we have had a lot of problems with pika, we want to be able to change to a different library e.g. pyAMPQ or rabbitpy without having to change the underlying code.

I was thinking of implementing something like this in the __init__.py file of servicelibrary.simple.

try:
    #import pika # Is pika installed?
    from servicelibrary.simple.synchronous import Publisher
    from servicelibrary.simple.synchronous import Consumer
except ImportError:
    #import ampq # Is ampq installed?
    from servicelibrary.simple.alternative import Publisher
    from servicelibrary.simple.alternative import Consumer

Then when the user imports the library

from servicelibrary.simple import Publisher

The underlying layer looks something like this

alternative.py

import amqp

class Publisher(object):
    ......

class Consumer(object):
     ......    

synchronous.py

import pika

class Publisher(object):
    ......

class Consumer(object):
     ......   

This would automatically pick the second one when the first one is not installed.

Is there a better way of implementing something like this? If anyone could link a library/adapter with a similar implementation that would be helpful as well.

[Edit]

What would be the cleanest way to implement something like this? In the future I would also like to be able to change the default preference. Ultimately I may just settle for using the library installed, as I can control that, but it would be a nice feature to have.

Alexanders suggestion is interesting, but I would like to know if there is a cleaner way.

[Edit2]

The original example was simplified. Each module may contain multiple types of imports, e.g. Consumer and Publisher.

Answer 1

The importlib.import_module might do what you need:

INSTALLED = ['syncronous', 'alternative']  

for mod_name in INSTALLED:
    try: 
        module = importlib.import_module('servicelibrary.simple.' + mod_name)
        Publisher = getattr(module, 'Publisher')

        if Publisher:
            break  # found, what we needed

    except ImportError:
        continue

I guess, this is not the most advance technique, but the idea should be clear. And you can take a look at the imp module as well.