Dependency Injection to modules

Question

Consider a module, e.g. some_module, that various modules use in the same interpreter process. This module would have a single context. In order for some_module methods to work, it must receive a dependency injection of a class instance.

What would be a pythonic and elegant way to inject the dependency to the module?

Answer 1

Use a module global.

import some_module
some_module.classinstance = MyClass()

some_module can have code to set up a default instance if one is not received, or just set classinstance to None and check to make sure it's set when the methods are invoked.

Answer 2

IMHo opinion full fledged Dependency Injection with all jargon is better suited to statically typed languages like Java, in python you can accomplish that very easily e.g here is a bare bone injection

class DefaultLogger(object):
   def log(self, line):
      print line

_features = {
   'logger': DefaultLogger
   }

def set_feature(name, feature):
   _features[name] = feature

def get_feature(name):
   return _features[name]()

class Whatever(object):

   def dosomething(self):
      feature = get_feature('logger')

      for i in range(5):
         feature.log("task %s"%i)

if __name__ == "__main__":
   class MyLogger(object):
      def log(sef, line):
         print "Cool",line

   set_feature('logger', MyLogger)

   Whatever().dosomething()

output:

Cool task 0
Cool task 1
Cool task 2
Cool task 3
Cool task 4

If you think something is missing we can add that easily, its python.