.. include:: ../common_links.inc

v3.5 (27 Apr 2023)
****************************************

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

.. dropdown:: v3.5 Release Highlights
   :color: primary
   :icon: info
   :animate: fade-in
   :open:

   The highlights for this major/minor release of Iris include:

   * We added support for plugins.
   * We allowed the usage of Iris objects as weights
     for cube aggregations.
   * We made Iris' use of the `netCDF4`_ library
     thread-safe.
   * We improved performance by changing the netCDF loader to
     fetch data immediately from small netCDF.
     variables, instead of creating a dask array.
   * We added notes within docstrings clarifying whether operations
     maintain lazy data or not.
   * We're so proud to fully support `@ed-hawkins`_ and `#ShowYourStripes`_ ❤️

   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
================

#. Congratulations to `@ESadek-MO`_ who has become a core developer for Iris! 🎉
#. Welcome and congratulations to `@HGWright`_, `@scottrobinson02`_ and
   `@agriyakhetarpal`_ who made their first contributions to Iris! 🎉


✨ Features
===========

#. `@bsherratt`_ added support for plugins - see the corresponding
   :ref:`documentation page<community_plugins>` for further information.
   (:pull:`5144`)

#. `@rcomer`_ enabled lazy evaluation of :obj:`~iris.analysis.RMS` calculations
   with weights. (:pull:`5017`)

#. `@schlunma`_ allowed the usage of cubes, coordinates, cell measures, or
   ancillary variables as weights for cube aggregations
   (:meth:`iris.cube.Cube.collapsed`, :meth:`iris.cube.Cube.aggregated_by`, and
   :meth:`iris.cube.Cube.rolling_window`). This automatically adapts cube units
   if necessary. (:pull:`5084`)

#. `@lbdreyer`_ and `@trexfeathers`_ (reviewer)  added :func:`iris.plot.hist`
   and :func:`iris.quickplot.hist`. (:pull:`5189`)

#. `@tinyendian`_ edited :func:`~iris.analysis.cartography.rotate_winds` to
   enable lazy computation of rotated wind vector components (:issue:`4934`,
   :pull:`4972`)

#. `@ESadek-MO`_ updated to the latest CF Standard Names Table v80
   (07 February 2023). (:pull:`5244`)


🐛 Bugs Fixed
=============

#. `@schlunma`_ fixed :meth:`iris.cube.CubeList.concatenate` so that it
   preserves derived coordinates. (:issue:`2478`, :pull:`5096`)

#. `@trexfeathers`_ and `@pp-mo`_ made Iris' use of the `netCDF4`_ library
   thread-safe. (:pull:`5095`)

#. `@ESadek-MO`_ removed check and error raise for saving
   cubes with masked :class:`iris.coords.CellMeasure`.
   (:issue:`5147`, :pull:`5181`)

#. `@scottrobinson02`_ fixed :class:`iris.util.new_axis` creating an anonymous new
   dimension, when the scalar coord provided is already a dim coord.
   (:issue:`4415`, :pull:`5194`)

#. `@HGWright`_ and `@trexfeathers`_ (reviewer) changed the way
   :class:`~iris.coords.CellMethod` are printed to be more CF compliant.
   (:pull:`5224`)

#. `@stephenworsley`_ fixed the way discontiguities were discovered for 2D coords.
   Previously, the only bounds being compared were the bottom right bound in one
   cell with the bottom left bound in the cell to its right, and the top left bound
   in a cell with the bottom left bound in the cell above it. Now all bounds are
   compared with all adjacent bounds from neighbouring cells. This affects
   :meth:`~iris.coords.Coord.is_contiguous` and :func:`iris.util.find_discontiguities`
   where additional discontiguities may be detected which previously were not.


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

#. N/A


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

#. `@pp-mo`_ changed the netCDF loader to fetch data immediately from small netCDF
   variables, instead of creating a dask array: This saves both time and memory.
   Note that some cubes, coordinates etc loaded from netCDF will now have real data
   where previously it was lazy.  (:pull:`5229`)


🔥 Deprecations
===============

#. N/A


🔗 Dependencies
===============

#. `@trexfeathers`_ introduced the ``libnetcdf <4.9`` pin. (:pull:`5242`)


📚 Documentation
================

#. `@rcomer`_ clarified instructions for updating gallery tests. (:pull:`5100`)
#. `@tkknight`_ unpinned ``pydata-sphinx-theme`` and set the default to use
   the light version (not dark) while we make the docs dark mode friendly
   (:pull:`5129`)

#. `@jonseddon`_ updated the citation to a more recent version of Iris. (:pull:`5116`)

#. `@rcomer`_ linked the :obj:`~iris.analysis.PERCENTILE` aggregator from the
   :obj:`~iris.analysis.MEDIAN` docstring, noting that the former handles lazy
   data. (:pull:`5128`)

#. `@trexfeathers`_ updated the WSL link to Microsoft's latest documentation,
   and removed an ECMWF link in the ``v1.0`` What's New that was failing the
   linkcheck CI. (:pull:`5109`)

#. `@trexfeathers`_ added a new top-level :doc:`/community/index` section,
   as a one-stop place to find out about getting involved, and how we relate
   to other projects. (:pull:`5025`)

#. The **Iris community**, with help from the **Xarray community**, produced
   the :doc:`/community/iris_xarray` page, highlighting the similarities and
   differences between the two packages. (:pull:`5025`)

#. `@bjlittle`_ added a new section to the `README.md`_ to show our support
   for the outstanding work of `@ed-hawkins`_ et al for `#ShowYourStripes`_.
   (:pull:`5141`)

#. `@HGWright`_ fixed some typo's from Gitwash. (:pull:`5145`)

#. `@Esadek-MO`_ added notes to function docstrings to
   to clarify if the function preserves laziness or not. (:pull:`5137`)

💼 Internal
===========

#. `@bouweandela`_ and `@trexfeathers`_ (reviewer) modernized and simplified
   the code of ``iris.analysis._Groupby``. (:pull:`5015`)

#. `@fnattino`_ changed the order of ``ncgen`` arguments in the command to
   create NetCDF files for testing  (caused errors on OS X). (:pull:`5105`)

#. `@rcomer`_ removed some old infrastructure that printed test timings.
   (:pull:`5101`)

#. `@lbdreyer`_ and `@trexfeathers`_ (reviewer) added coverage testing. This
   can be enabled by using the "--coverage" flag when running the tests with
   nox i.e. ``nox --session tests -- --coverage``. (:pull:`4765`)

#. `@lbdreyer`_ and `@trexfeathers`_ (reviewer) removed the ``--coding-tests``
   option from Iris' test runner. (:pull:`4765`)

#. `@lbdreyer`_ removed the Iris TestRunner. Tests are now run via nox or
   pytest. (:pull:`5205`)

#. `@agriyakhetarpal`_ and `@trexfeathers`_ prevented the GitHub action for
   publishing releases to PyPI from running in forks.
   (:pull:`5220`, :pull:`5248`)

#. `@trexfeathers`_ moved the benchmark runner conveniences from ``noxfile.py``
   to a dedicated ``benchmarks/bm_runner.py``. (:pull:`5215`)

#. `@bjlittle`_ follow-up to :pull:`4972`, enforced ``dask>=2022.09.0`` minimum
   pin for first use of `dask.array.ma.empty_like`_ and replaced `@tinyendian`_
   workaround. (:pull:`5225`)

#. `@HGWright`_, `@bjlittle`_ and `@trexfeathers`_ removed the legacy pin for
   ``numpy`` array printing and replaced the test results files to match default
   ``numpy`` output. (:pull:`5235`)


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

.. _@fnattino: https://github.com/fnattino
.. _@ed-hawkins: https://github.com/ed-hawkins
.. _@scottrobinson02: https://github.com/scottrobinson02
.. _@agriyakhetarpal: https://github.com/agriyakhetarpal
.. _@tinyendian: https://github.com/tinyendian


.. comment
    Whatsnew resources in alphabetical order:

.. _#ShowYourStripes: https://showyourstripes.info/s/globe/
.. _README.md: https://github.com/SciTools/iris#-----
.. _dask.array.ma.empty_like: https://docs.dask.org/en/stable/generated/dask.array.ma.empty_like.html