@@ -122,6 +122,12 @@ Importing ``parent.one`` will implicitly execute ``parent/__init__.py`` and
122122``parent.three`` will execute ``parent/two/__init__.py`` and
123123``parent/three/__init__.py`` respectively.
124124125+A subdirectory inside a regular package that does not contain an
126+``__init__.py`` file is treated as an implicit
127+:ref:`namespace package <reference-namespace-package>` (a "namespace
128+subpackage") rooted in that parent. See :pep:`420` for the underlying
129+specification.
130+125131126132.. _reference-namespace-package:
127133@@ -153,6 +159,12 @@ physically located next to ``parent/two``. In this case, Python will create a
153159namespace package for the top-level ``parent`` package whenever it or one of
154160its subpackages is imported.
155161162+Namespace packages may also be nested inside a regular package. When the
163+import system searches a regular package's ``__path__`` and encounters a
164+subdirectory that does not contain an ``__init__.py`` file, that
165+subdirectory becomes a :term:`portion` contributing to a namespace
166+subpackage of the enclosing regular package.
167+156168See also :pep:`420` for the namespace package specification.
157169158170