subpackage

Subpackage refers to a package that is contained within another package, forming a hierarchical namespace used to organize code and related resources. A subpackage shares the same top-level package name, enabling a modular structure and easier management of large codebases.

Different programming ecosystems treat subpackages with slightly different terminology. In Python, a directory containing an __init__.py file constitutes a package; subdirectories under that package define subpackages, accessible via import statements like mypkg.utils.parser. Since Python 3.3, namespace packages allow subpackages without an __init__ file in certain cases. In Java, packages are hierarchical by convention through dot-separated names, such as com.example and com.example.util; the term subpackage is informal, referring to deeper levels of the package name, all packaged together in a JAR. In Go, packages live under directories and import paths express the package path; subdirectories under a module can form subpackages. In C#, nested namespaces serve a similar role, though the term subpackage is less common.

In distribution packaging, many ecosystems use the term subpackage to describe a distinct binary component of a larger logical package, for example splitting a library into a runtime package and a data package.

Benefits of subpackages include namespace isolation, clearer dependency boundaries, and easier reuse and testing. Potential drawbacks include management overhead and the risk of deep hierarchies or circular imports.

When designing a project, use subpackages to group related functionality with a cohesive API surface, maintain stable public interfaces, and keep internal details private to each subpackage where appropriate.