initpy

Initpy is a term used in Python programming to refer to the initialization script init.py inside a package directory. The presence of this file marks the directory as a Python package and makes its contents importable as module attributes. When a package is imported, Python executes the code at the top level of init.py, which commonly sets up package-level state, defines public API symbols, and imports frequently used submodules.

Typical contents include import statements for submodules, assignment to all, version information, and small initialization routines. The file may be empty or contain minimal code, especially if the package relies on lazy imports for its submodules.

Namespace packages: Python 3.3+ supports implicit namespace packages (PEP 420). A directory without init.py can be part of a namespace package if multiple locations share the same name. Conversely, a directory containing init.py is a regular package, and its init.py runs on import. Having init.py can also facilitate compatibility with older tooling.

Best practices: keep init.py lightweight; avoid heavy I/O or long-running initialization; use all to define public API; consider delaying submodule imports to optimize startup time; document the intended public API. See also: init.py, Python packaging, PEP 420.