.. include:: ../common_links.inc

v3.9 (22 Apr 2024)
******************

This document explains the changes made to Iris for this release
(:doc:`View all changes <index>`.)


.. dropdown:: v3.9 Release Highlights
   :color: primary
   :icon: info
   :animate: fade-in
   :open:

   This is a small release to make two important changes available as soon as
   possible:

   * The :mod:`iris.experimental.geovista` module.
   * Removal of fill value collision warnings in NetCDF saving, which
     significantly improves Iris' performance when parallel processing.

   See below for more detail on these changes.

   And finally, get in touch with us on :issue:`GitHub<new/choose>` if you have
   any issues or feature requests for improving Iris. Enjoy!


📢 Announcements
================

#. ⏱️ Performance benchmarking has shown that loading
   :term:`Fields File (FF) Format` with a large number of fields via
   :func:`iris.fileformats.um.structured_um_loading` has become ~30% slower
   since `Dask version 2024.2.1`_.


✨ Features
===========

#. `@HGWright`_ and `@trexfeathers`_ added the
   :mod:`iris.experimental.geovista` module, providing conveniences for using
   :ref:`ugrid geovista` with Iris. To see some of this in action, check out
   :ref:`ugrid operations`. Note that GeoVista is an **optional** dependency
   so you will need to explicitly install it into your environment.
   (:pull:`5740`)


🐛 Bugs Fixed
=============

#. `@pp-mo`_ prevented the CHUNK_CONTROL feature from hitting an error when loading
   from a NetCDF v3 file.  (:pull:`5897`)


💣 Incompatible Changes
=======================

#. Warnings are no longer produced for fill value 'collisions' in NetCDF
   saving. :ref:`Read more <missing_data_saving>`. (:pull:`5833`)


🚀 Performance Enhancements
===========================

#. `@bouweandela`_ made :func:`iris.util.rolling_window` work with lazy arrays.
   (:pull:`5775`)

#. `@stephenworsley`_ fixed a potential memory leak for Iris uses of
   :func:`dask.array.map_blocks`; known specifically to be a problem in the
   :class:`iris.analysis.AreaWeighted` regridder. (:pull:`5767`)

#. `@fnattino`_ and `@pp-mo`_ prevented cube printout from showing the values of lazy
   scalar coordinates, since this can involve a lengthy computation that must be
   re-computed each time.  (:pull:`5896`)


🔥 Deprecations
===============

#. N/A


🔗 Dependencies
===============

#. `@bjlittle`_ dropped support for ``py39`` and adopted support for ``py312`` as per
   the `NEP-29`_ schedule. (:pull:`5894`)


📚 Documentation
================

#. N/A


💼 Internal
===========

#. `@trexfeathers`_ setup automatic benchmarking on pull requests that modify
   files likely to affect performance or performance testing. Such pull
   requests are also labelled using the `Pull Request Labeler Github action`_
   to increase visibility. (:pull:`5763`, :pull:`5776`)

#. `@tkknight`_ updated codebase to comply with a new enforced rule `NPY002`_ for
   `ruff`_.  (:pull:`5786`)

#. `@tkknight`_ enabled `numpydoc validation`_ via the pre-commit hook.  The docstrings
   have been updated to comply and some rules have been ignored for now.
   (:pull:`5762`)

#. `@jfrost-mo`_ enabled colour output for pytest on GitHub Actions. (:pull:`5895`)


.. comment
    Whatsnew author names (@github name) in alphabetical order. Note that,
    core dev names are automatically included by the common_links.inc:

.. _@jfrost-mo: https://github.com/jfrost-mo
.. _@fnattino: https://github.com/fnattino


.. comment
    Whatsnew resources in alphabetical order:

.. _Pull Request Labeler GitHub action: https://github.com/actions/labeler
.. _NPY002: https://docs.astral.sh/ruff/rules/numpy-legacy-random/
.. _numpydoc validation: https://numpydoc.readthedocs.io/en/latest/validation.html#
.. _Dask version 2024.2.1: https://docs.dask.org/en/stable/changelog.html#v2024-2-1
.. _NEP-29: https://numpy.org/neps/nep-0029-deprecation_policy.html#drop-schedule