Question

I want to parse an Apache access.log file with a python program in a certain way, and though I am completely new to object-oriented programming, I want to start doing it now.

I am going to create a class ApacheAccessLog, and the only thing I can imagine now, it will be doing is ‘readline‘ method. Is it conventionally correct to inherit from the builtin file class in this case, so the class will behave just like an instance of the file class itself, or not? What is the best way of doing that?

Answer 1

In this case I would use delegation rather than inheritance. It means that your class should contain the file object as an attribute and invoke a readline method on it. You could pass a file object in the constructor of the logger class.

There are at least two reasons for this:

1. Delegation reduces coupling, for example in place of file objects you can use any other object that implements a readline method (duck typing comes handy here).
2. When inheriting from file the public interface of your class becomes unnecessarily broad. It includes all the methods defined on file even if these methods don’t make sense in case of Apache log.