dau_core._lazy
==============

.. py:module:: dau_core._lazy

.. autoapi-nested-parse::

   Import a package's exports on first use.

   Every model in this stack is a ccflow model, and importing ccflow imports
   csp, pandas and the rest of its stack: about 0.9 s. A package whose
   ``__init__`` imports its model modules therefore pays all of it just to be
   imported -- including when hydra's searchpath plugin imports the config
   package to discover what is installed, which is the slow step in composing
   the registry and wants none of those names.

   So a package declares which submodule provides each exported name and this
   builds the ``__getattr__`` that imports the one submodule the name needs.
   The names stay importable exactly as before (``from dau_core import
   RegisterOffset``), and a type checker reads them from the ``TYPE_CHECKING``
   block the package keeps beside the declaration.



Functions
---------

.. autoapisummary::

   dau_core._lazy.lazy_exports


Module Contents
---------------

.. py:function:: lazy_exports(package: str, exports: dict[str, tuple[str, ...]]) -> tuple[collections.abc.Callable[[str], object], list[str]]

   A module ``__getattr__`` and ``__all__`` for ``{submodule: names}``.

   Returns both so the two cannot disagree: a name exported by nothing is
   not reachable, and a name declared here and missing from its submodule
   raises on first access rather than at import, which a guard test is what
   turns back into an import-time error.