.. _skim:

=====
Skims
=====

The skim package is a collection of high-level analysis scripts that reduce the data set to a manageable size by applying a simple selection.
The input to a skim are :ref:`mdst` files of processed data.
The output are so-called :ref:`analysis_udstoutput` (udst) files.
These files actually contain more information but fewer events.

.. tip:: Analysts are recommended to use skimmed udst files as input to their analysis. For an introductory lesson, take a look at :numref:`onlinebook_skim`.

.. tip:: If you would like to know which skims are available, please browse the :ref:`skim_physics` section of the documentation. If you would like to know which cuts are made by a particular skim, then consult the source code by clicking the ``[source]`` button on that skim in :ref:`skim_physics`, or by navigating to ``skim/scripts/skim/WGs/<your working group name>/`` in the basf2 repository.

.. versionchanged:: release-06-00-00

    The skim package was reorganised between releases 5 and 6. If you need your skim steering files to work with both release 5 and release 6, then please use the following type of try-except block:

    .. code-block:: python

        try:
            # release 6+ imports
            from skim import BaseSkim, CombinedSkim
            from skim.WGs.ewp import BtoXll
        except (ImportError, ModuleNotFoundError):
            # release 5 imports
            from skimExpertFunctions import BaseSkim, CombinedSkim
            from skim.ewp import BtoXll

.. toctree::
    01-systematics
    02-physics
    03-lists
    04-experts