Inject class to Python module dynamically

As you probably know in Python after you import some module you may call functions defined in this module. But if you work with more complex scenarios (e.g. when imported module is provided automatically by infrastructure (i.e. you don't control it) or when classes are generated in runtime using Python meta classes) you may face with situation when some class is missing in imported module. In this case Python will show the following error:

AttributeError: module 'SomeExternalModule' has no attribute 'SomeAPI'

(in this example we assume that module name is SomeExternalModule and class name is SomeAPI). Of course if you need functionality defined in missing class you have to resolve this issue properly to ensure that missing class will exist in imported module. But if it is not critical and you just want to pass through these calls you may use trick with injecting class to module dynamically. E.g. class with single static method (method without "self" first argument) can be added to module like that:

def Log(msg):
    print(msg)

SomeExternalModule.SomeAPI = type("SomeAPI", (object, ), {
    "Log": Log
})

Here we injected class SomeAPI to module SomeExternalModule. Class contains one method called Log which just prints message to console. In addition to static methods we may also add instance methods using similar technique - just add "self" first argument to the method in this case.

After that if you will run code which relies on SomeExternalModule.SomeAPI() calls error should gone.