Define Classes in Packages

Question

I'm learning Python and I have been playing around with packages. I wanted to know the best way to define classes in packages. It seems that the only way to define classes in a package is to define them in the __init__.py of that package. Coming from Java, I'd kind of like to define individual files for my classes. Is this a recommended practice?

I'd like to have my directory look somewhat like this:

recursor/
 __init__.py
 RecursionException.py
 RecursionResult.py
 Recursor.py

So I could refer to my classes as recursor.Recursor, recursor.RecursionException, and recursor.RecursionResult. Is this doable or recommended in Python?

• Esteban Küber: Obligatory: Python is not Java
• froadie: Also check out stackoverflow.com/questions/2339371/…
• user97370: Yes you can, but no you shouldn't.

Answer 1

Go ahead and define your classes in separate modules. Then make __init__.py do something like this:

from RecursionException import RecursionException
from RecursionResult import RecursionResult
from Recursor import Recursor

That will import each class into the package's root namespace, so calling code can refer to recursor.Recursor instead of recursor.Recursor.Recursor.

I feel the need to echo some of the other comments here, though: Python is not Java. Rather than creating a new module for every class under the sun, I suggest grouping closely related classes into a single module. It's easier to understand your code that way, and calling code won't need a bazillion imports.

• user657199: Although recursor.Recursor.Recursor does have certain charm to it.

Answer 2

This is perfectly doable. Just create a new class module for each of those classes, and create exactly the structure you posted.

You can also make a Recursion.py module or something similar, and include all 3 classes in that file.

(I'm also new to Python from Java, and I haven't yet put anything in my __init__.py files...)

• Naftuli Kay: If I create the directory layout above, defining my Recursor class in the Recursor.py file and I try to import "recursor.Recursor," I get an ImportError. What am I doing wrong?
• froadie: @rfkrocktk - you may have to specify recursor.Recursor.Recursor... the first for the package, the second for the module (the file), and the third for the actual class... (It's sometimes better to consider using modules sort of as packages... instead of a package recursor with these 3 classes as separate files, you can have a module recursor with these 3 classes inside it)

Answer 3

In Python you're not restricted to defining 1 class per file and few do that. You can if you want to though - it's totally up to you. A Package in Python is just a directory with an

__init__.py 

file. You don't have to put anything in that file you can to control what gets imported etc.