Question

I am trying to give a slight amount of genericness to my code . Basically what I am looking for is this .

I wish to write an API interface MyAPI :

class MyAPI(object):
    def __init__(self):
       pass

    def upload(self):
       pass

    def download(self):
      pass

class MyAPIEx(object):
   def upload(self):
      #specific implementation

class MyAPIEx2(object): 
   def upload(self)
    #specific implementation

#Actual usage ... 
def use_api():
     obj = MyAPI()
     obj.upload()

SO what I want is that based on a configuration I should be able to call the upload function
of either MyAPIEx or MyAPIEx2 . What is the exact design pattern I am looking for and how do I implement it in python.

Answer 1

Its really hard to say what pattern you are using, without more info. The way to instantiate MyAPI is indeed a Factory like @Darhazer mentioned, but it sounds more like you’re interested in knowing about the pattern used for the MyAPI class hierarchy, and without more info we cant say.

I made some code improvements below, look for the comments with the word IMPROVEMENT.

class MyAPI(object):
    def __init__(self):
       pass

    def upload(self):
       # IMPROVEMENT making this function abstract
       # This is how I do it, but you can find other ways searching on google
       raise NotImplementedError, "upload function not implemented"

    def download(self):
       # IMPROVEMENT making this function abstract
       # This is how I do it, but you can find other ways searching on google
       raise NotImplementedError, "download function not implemented"

# IMPROVEMENT Notice that I changed object to MyAPI to inherit from it
class MyAPIEx(MyAPI):
   def upload(self):
      #specific implementation

# IMPROVEMENT Notice that I changed object to MyAPI to inherit from it
class MyAPIEx2(MyAPI): 
   def upload(self)
      #specific implementation


# IMPROVEMENT changed use_api() to get_api(), which is a factory,
# call it to get the MyAPI implementation
def get_api(configDict):
     if 'MyAPIEx' in configDict:
         return MyAPIEx()
     elif 'MyAPIEx2' in configDict:
         return MyAPIEx2()
     else
         # some sort of an error

# Actual usage ... 
# IMPROVEMENT, create a config dictionary to be used in the factory
configDict = dict()
# fill in the config accordingly
obj = get_api(configDict)
obj.upload()