Question

I’m using a Builder pattern in Python to separate a bunch of different configuration possibilities. Basically, I have a bunch of classes that are named ID... (e.g. ID12345). These all inherit from the base Builder class. In my script, I need to instantiate an instance for each class (about 50) every time this app runs. So, I’m trying to see if instead of doing something like this:

ProcessDirector = ProcessDirector() ID12345 = ID12345() ID01234 = ID01234()  ProcessDirector.construct(ID12345) ProcessDirector.construct(ID01234)  ID12345.run() ID01234.run() 

Can I do something like this (I know this doesn’t work):

IDS = ["ID12345", "ID01234"]  ProcessDirector = ProcessDirector() for id in IDS:   builder = id() #some how instantiate class from string   ProcessDirector.construct(builder)   builder.run() 

That way, when I need to add a new one in the future, all I have to do is add the id to the IDS list, rather than peppering the new ID throughout the code.

EDIT:

Looks like there are different opinions based on where the data is coming from. These IDs are entered in a file that no one else has access to. I’m not reading the strings from the command line, and I’d like to be able to do as little alteration when adding a new ID in the future.

Answer 1

Not sure this is what you want but it seems like a more Pythonic way to instantiate a bunch of classes listed in a string:

class idClasses:     class ID12345:pass     class ID01234:pass # could also be: import idClasses  class ProcessDirector:     def __init__(self):         self.allClasses = []      def construct(self, builderName):         targetClass = getattr(idClasses, builderName)         instance = targetClass()         self.allClasses.append(instance)  IDS = ['ID12345', 'ID01234']  director = ProcessDirector() for id in IDS:     director.construct(id)  print director.allClasses # [<__main__.ID12345 instance at 0x7d850>, <__main__.ID01234 instance at 0x7d918>]