Question

Coming to Python from Java, I’ve been told that factories are not Pythonic. Thus, I’m looking for a the Python way to do something like the following. (I’m oversimplifying my goal so that I don’t have to describe my entire program, which is very complicated).

My script will read in names of people (along with some information about them) and, from this, construct objects of type Person. The names may be repeated, and I only want one Person instance per name. These People may also belong to subclasses Man and Woman.

One way to do this would be to create a PersonFactory which would either return a newly instantiated Man or Woman or a reference to the previously instantiated Man/Woman with the same name. The other would be to create a set of all Person objects and check each time for the presence of a Person with the given name before instantiating a new object. Neither approach strikes me as Pythonic, though. The first seems a bit too cumbersome for Python (creating a whole class just to handle creation of another object? Really?) and the second will get expensive quickly, as I have a lot of names to process.

Answer 1

I don’t think factories are un-Pythonic. You don’t need a whole class, though. One big difference between Java and Python is that in Python you can have code outside of classes. So you might want to create a factory function. Or you can make the factory be a class method on the Person class:

class Person:

    name_map = {}

    @classmethod
    def person_from_name(cls, name):
        if name not in cls.name_map:
            cls.name_map[name] = cls(name)
        return cls.name_map[name]

    def __init__(self, name):
        etc...

Often the same patterns are at work in Python code as in Java, but we don’t make as big a deal of it. In Java, you’d have a whole new class, which would imply a whole new .java file, and you’d need to make it a singleton, etc, etc. Java seems to breed this sort of complexity. A simple class method will do, so just use it.