Is __init__.py not required for packages in Python 3.3+?

From Python 3.3 onward, namespace packages allow you to create a package-like structure without necessarily including an __init__.py file. This feature was introduced as part of PEP 420 to make it easier to split the same “logical” package across multiple directories or distributions.

However, whether you do or don’t need an __init__.py file depends on what you’re trying to achieve:

1. Traditional Packages

   • In most cases, you still use an __init__.py file to indicate that a directory is a regular Python package. This file can be empty or can contain initialization code that executes when the package is imported.
   • If you rely on package-level variables or need to execute startup logic, an __init__.py is still necessary.

2. Namespace Packages

   • Namespace packages allow multiple directories (spread across the filesystem or different distributions) to be merged into one logical package namespace without requiring an __init__.py.
   • They are especially useful in larger projects or plugin-like systems where different modules may live in separate repositories but share a common top-level package name.

3. Practical Consequences

   • For small-to-medium projects, most developers still include __init__.py to avoid confusion and to keep a consistent project layout.
   • If you’re building a project with sub-packages spread across multiple locations, or you’re releasing libraries that others can add to, namespace packages might be the better approach.

Example of a Namespace Package

Imagine you have a top-level package mytools, which is split between two directories:

# Directory A
mytools/              <-- no __init__.py here
    utils.py

# Directory B
mytools/              <-- also no __init__.py here
    extra.py

With Python 3.3+ and PEP 420, you can import both mytools.utils and mytools.extra as if they were in the same package—even though there’s no __init__.py.

Best Practices

• Keep an __init__.py if you want a traditional package or you have package initialization code that needs to run on import.
• Skip __init__.py if you’re intentionally creating a namespace package and want to merge multiple directories or distributions under the same namespace.

Where to Learn More

If you’re looking to broaden your Python knowledge beyond package organization, these courses from DesignGurus.io may help:

• Grokking Python Fundamentals
  Covers everything from Python basics to advanced concepts, ensuring you understand how and why features like namespace packages exist.

• Grokking the Coding Interview: Patterns for Coding Questions
  Focuses on the critical patterns behind solving coding problems—ideal if you plan to use Python in tech interviews.

Beyond coding, if you’re aiming to build scalable software or prepare for system design interviews, consider:

• Grokking System Design Fundamentals
  A great introduction to designing robust, high-performance applications—vital knowledge for developers in top tech roles.

Key Takeaway:
__init__.py is not strictly required for namespace packages in Python 3.3+, but it’s still used in many traditional packages to define initialization code and maintain a predictable project structure.