Why would I put code in __init__.py files?

Question

I am looking for what type of code would I put in __init__.py files and what are the best practices related to this. Or, is it a bad practice in general ?

Any reference to known documents that explain this is also very much appreciated.

Answer 1

Libraries and frameworks usually use initialization code in __init__.py files to neatly hide internal structure and provide a uniform interface to the user.

Let's take the example of Django forms module. Various functions and classes in forms module are defined in different files based on their classification.

forms/   __init__.py   extras/     ...   fields.py   forms.py   widgets.py   ... 

Now if you were to create a form, you would have to know in which file each function is defined and your code to create a contact form will have to look something like this (which is incovenient and ugly).

 class CommentForm(forms.forms.Form):     name = forms.fields.CharField()      url = forms.fields.URLField()     comment = forms.fields.CharField(widget=forms.widgets.Textarea)  

Instead, in Django you can just refer to various widgets, forms, fields etc. directly from the forms namespace.

from django import forms  class CommentForm(forms.Form):     name = forms.CharField()     url = forms.URLField()     comment = forms.CharField(widget=forms.Textarea) 

How is this possible? To make this possible, Django adds the following statement to forms/__init__.py file which import all the widgets, forms, fields etc. into the forms namespace.

from widgets import * from fields import * from forms import * from models import * 

As you can see, this simplifies your life when creating the forms because now you don't have to worry about in where each function/class is defined and just use all of these directly from forms namespace. This is just one example but you can see examples like these in other frameworks and libraries.