lenskit.lazy.Lazy
=================

.. py:class:: lenskit.lazy.Lazy[T]
   

   Bases: :py:obj:`Protocol`


   Type for lazily-computed values.

   This is frequently used in pipeline components.  If a pipeline component
   may or may not need one of its inputs, declare the type with this to only
   run it as needed:

   .. code:: python

       def my_component(input: str, backup: Lazy[str]) -> str:
           if input == 'invalid':
               return backup.get()
           else:
               return input

   :Stability: Caller


   .. py:method:: get()

      Get the value behind this lazy instance.

      .. note::

          When used as a pipeline input this method invokes upstream
          components if they have not yet been run.  Therefore, it may fail if
          one of the required components fails or pipeline data checks fail.

      :raises Exception: Exceptions raised by sources of the lazy data (e.g. a thunk, or
          upstream components) may be raised when this method is called.
      :raises SkipComponent: Internal exception raised to indicate that no value is available
          and the calling component should be skipped.  Components
          generally do not need to handle this directly, as it is used to
          signal the pipeline runner.
          
          Only raised when used as a pipeline input.