Do I Need `__init__.py` Files for Packages in Python 3.3 ?

Namespace Packages in Python 3.3

Question:

In Python 3.3 , is it still necessary to have an __init__.py file when importing packages?

Answer:

Not necessarily. Python 3.3 introduced the concept of "Implicit Namespace Packages," allowing packages to be created without an __init__.py file. These are known as namespace packages, in contrast to regular packages that do have an __init__.py file.

Implicit Namespace Package Use Case:

Namespace packages are specifically used when multiple libraries reside in different locations and need to contribute a subpackage to the same parent package. For example, consider the following structure:

google_pubsub/             # Package 1
    google/                 # Namespace package
        cloud/              # Namespace package
            pubsub/         # Regular package
                __init__.py
                foo.py

google_storage/             # Package 2
    google/                 # Namespace package
        cloud/              # Namespace package
            storage/        # Regular package
                __init__.py
                bar.py

Without namespace packages, importing both "google_pubsub" and "google_storage" would fail because Python treats regular packages as self-contained entities. By removing the __init__.py files from the "google" and "google/cloud" directories, they are interpreted as namespace packages, allowing the Python interpreter to find and contribute modules and subpackages to the "google" package.

Regular vs. Namespace Packages:

In most cases, it's recommended to stick with regular packages by using empty __init__.py files. This is because:

• Regular packages are more predictable and easier to maintain.
• Many Python tools and libraries expect regular packages to function properly.

Conclusion:

While namespace packages can be useful in specific scenarios, they should be used sparingly. For most developers and use cases, regular packages with __init__.py files are the recommended approach. Consider namespace packages only when there is a genuine need for sharing namespaces between multiple directories containing subpackages.

References:

• [PEP 420 - Implicit Namespace Packages](https://www.python.org/dev/peps/pep-0420/)
• [Python Docs - Regular Packages](https://docs.python.org/3/reference/import.html#packages)
• [Python Docs - Namespace Packages](https://docs.python.org/3/reference/import.html#namespace-packages)
• [Traps for the Unwary in Python's Import System](https://www.python.org/doc/essays/import-traps/)

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