Question: I am using Popen to run a command but I don't know how I can write a callback that gets called once the command is finished. Any idea?

Thanks.
Bin

Answer: 
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.
The place to put a "no two objects with same key" registration is in `__new__`, like this:

```
class Person(object):
    person_registry = {}
    mens_names = set('Tom Dick Harry'.split())
    womens_names = set('Mary Linda Susan'.split())
    gender = "?"
    def __new__(cls, *args):
        if cls is Person:
            fname,lname = args[0].split()
            key = (lname, fname)
            if key in Person.person_registry:
                return Person.person_registry[key]

            if fname in Person.mens_names:
                return Man(*args)
            if fname in Person.womens_names:
                return Woman(*args)
        else:
            return object.__new__(cls, *args)

    def __init__(self, name):
        fname,lname = name.split()
        Person.person_registry[(lname, fname)] = self

class Man(Person):
    gender = "M"

class Woman(Person):
    gender = "W"

p1 = Person("Harry Turtledove")
print p1.__class__.__name__, p1.gender

p2 = Person("Harry Turtledove")

print p1 is p2

```

prints:

```
Man M
True

```

I also took a stab at your Man/Woman distinction, but I'm not thrilled with it.