How to Create Namespace Packages for Multiple Python Products?

Defining Namespace Packages for Multiple Python Products

In Python, namespace packages enable the distribution of related libraries in separate downloads. This allows multiple Python products to define modules within the same namespace.

Problem Overview

How can we effectively create a namespace package that allows more than one Python product to define modules in that namespace?

TL;DR

In Python 3.3 and above, implicit namespace packages alleviate the need for any special steps. In earlier versions, utilizing the pkgutil.extend_path() solution is recommended over pkg_resources.declare_namespace() due to its compatibility with implicit namespace packages.

Detailed Solution

Prior to Python 3.3, the pkg_resources.declare_namespace() function was used to create namespace packages. However, with the introduction of implicit namespace packages in Python 3.3, the pkgutil.extend_path() method has become the preferred approach. This approach can also handle both implicit and explicit namespace packages, making it future-proof.

The extend_path() method modifies the __path__ attribute of an existing regular package to include additional paths. In this way, modules from different namespace packages can be imported under the same namespace.

For example, consider the following directory structure:

├── path1
│   └── package
│       ├── __init__.py
│       └── foo.py
├── path2
│   └── package
│       └── bar.py
└── path3
    └── package
        ├── __init__.py
        └── baz.py

To make these directories accessible as part of the namespace package, the following code can be added to the __init__.py files of the regular packages in path1 and path3:

<code class="python">from pkgutil import extend_path
__path__ = extend_path(__path__, __name__)</code>

With this solution, the following imports will be successful:

<code class="python">import package.foo
import package.bar
import package.baz</code>

Using the pkgutil.extend_path() method allows namespace packages to be created and managed effectively, enabling multiple Python products to utilize code within the same namespace.

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