Demystifying the init python file

When we’re developing our application, we have to oftentimes create a special file: __init__.py. What is this file, why is it important, and why would I put code in here?

Sometimes, it’s completely empty. Othertimes, you’ll see import statements, functions, and even classes in the init file.

I’m going to provide a simple explanation on how this file works by giving a practical example using the Flask Github repository.

What is the role of __init__.py?

This file tells the Python interpreter that the files that are in the same directory are all related to one another. This file does 3 things for us as developers:

1. Recognizes code as a package rather than individual files

2. Organizes code to tell developers what other code to expose to the outside world,

3. Initializes any variables and objects that are needed for that package.

Practical Example: Flask

Let’s take a look at a very popular micro-web framework application: Flask.

If we were to import Flask into our python code (import flask), we’re saying “I want to use everything Flask has to offer”. However, Python doesn’t really know what it has to offer, and that’s where __init__.py comes into play.

What’s happening under the hood is that Python recognizes all of the files located under the src/flask directory in the repository as what you want to import:

» Prior to Python 3.3, you wouldn’t be able to access any of the code that Flask offers. You now don’t need to have this file, but there’s drawbacks to this.

Do I need code in the init file?

You necessarily don’t need code, but it helps with cleaning up imports and initializing any objects you may want the user to have.

Let’s continue looking at the __init__.py file. Inside of it, we have a ton of import statements from this directory:

I want to highlight one of the imports on line 23: send_file. This function is located in helpers.py.

Because the developers are importing it in the __init__.py file, we can import this specific function as from flask import send_file.

Without the __init__.py file, we would have to import this function as from flask.helpers import send_file.

Hope this clears things up. Happy coding!