.. _whats-new-2-2-0:

What's new in Matplotlib 2.2 (Mar 06, 2018)
===========================================

Constrained Layout Manager
--------------------------

.. warning::

    Constrained Layout is **experimental**.  The
    behaviour and API are subject to change, or the whole functionality
    may be removed without a deprecation period.


A new method to automatically decide spacing between subplots and their
organizing ``GridSpec`` instances has been added.  It is meant to
replace the venerable ``tight_layout`` method.  It is invoked via
a new ``constrained_layout=True`` kwarg to
`~.figure.Figure` or `~.Figure.subplots`.

There are new `.rcParams` for this package, and spacing can be
more finely tuned with the new `~.set_constrained_layout_pads`.

Features include:

- Automatic spacing for subplots with a fixed-size padding in inches around
  subplots and all their decorators, and space between as a fraction
  of subplot size between subplots.
- Spacing for `~.Figure.suptitle`, and colorbars that are attached to
  more than one axes.
- Nested `~.GridSpec` layouts using `~.GridSpecFromSubplotSpec`.

For more details and capabilities please see the new tutorial:
:ref:`constrainedlayout_guide`

Note the new API to access this:

New ``plt.figure`` and ``plt.subplots`` kwarg: ``constrained_layout``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

:meth:`~matplotlib.pyplot.figure` and :meth:`~matplotlib.pyplot.subplots`
can now be called with ``constrained_layout=True`` kwarg to enable
constrained_layout.

New ``ax.set_position`` behaviour
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`.Axes.set_position` now makes the specified axis no
longer responsive to ``constrained_layout``, consistent with the idea that the
user wants to place an axis manually.

Internally, this means that old ``ax.set_position`` calls *inside* the library
are changed to private ``ax._set_position`` calls so that
``constrained_layout`` will still work with these axes.

New ``figure`` kwarg for ``GridSpec``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In order to facilitate ``constrained_layout``, ``GridSpec`` now accepts a
``figure`` keyword.  This is backwards compatible, in that not supplying this
will simply cause ``constrained_layout`` to not operate on the subplots
organized by this ``GridSpec`` instance.  Routines that use ``GridSpec`` (e.g.
``fig.subplots``) have been modified to pass the figure to ``GridSpec``.


xlabels and ylabels can now be automatically aligned
----------------------------------------------------

Subplot axes ``ylabels`` can be misaligned horizontally if the tick labels
are very different widths.  The same can happen to ``xlabels`` if the
ticklabels are rotated on one subplot (for instance).  The new methods
on the `.Figure` class: `.Figure.align_xlabels` and `.Figure.align_ylabels`
will now align these labels horizontally or vertically.  If the user only
wants to align some axes, a list of axes can be passed.  If no list is
passed, the algorithm looks at all the labels on the figure.

Only labels that have the same subplot locations are aligned.  i.e. the
ylabels are aligned only if the subplots are in the same column of the
subplot layout.

Alignment is persistent and automatic after these are called.

A convenience wrapper `.Figure.align_labels` calls both functions at once.

.. plot::

    import matplotlib.gridspec as gridspec

    fig = plt.figure(figsize=(5, 3), tight_layout=True)
    gs = gridspec.GridSpec(2, 2)

    ax = fig.add_subplot(gs[0,:])
    ax.plot(np.arange(0, 1e6, 1000))
    ax.set_ylabel('Test')
    for i in range(2):
        ax = fig.add_subplot(gs[1, i])
        ax.set_ylabel('Booooo')
        ax.set_xlabel('Hello')
        if i == 0:
            for tick in ax.get_xticklabels():
                tick.set_rotation(45)
    fig.align_labels()


Axes legends now included in tight_bbox
---------------------------------------

Legends created via ``ax.legend`` can sometimes overspill the limits of
the axis.  Tools like ``fig.tight_layout()`` and
``fig.savefig(bbox_inches='tight')`` would clip these legends.  A change
was made to include them in the ``tight`` calculations.


Cividis colormap
----------------

A new dark blue/yellow colormap named 'cividis' was added. Like
viridis, cividis is perceptually uniform and colorblind
friendly. However, cividis also goes a step further: not only is it
usable by colorblind users, it should actually look effectively
identical to colorblind and non-colorblind users. For more details
see `Nuñez J, Anderton C, and Renslow R: "Optimizing colormaps with consideration
for color vision deficiency to enable accurate interpretation of scientific data"
<https://doi.org/10.1371/journal.pone.0199239>`_.

.. plot::

    import matplotlib.pyplot as plt
    import numpy as np

    fig, ax = plt.subplots()
    pcm = ax.pcolormesh(np.random.rand(32,32), cmap='cividis')
    fig.colorbar(pcm)


New style colorblind-friendly color cycle
-----------------------------------------

A new style defining a color cycle has been added,
tableau-colorblind10, to provide another option for
colorblind-friendly plots.  A demonstration of this new
style can be found in the reference_ of style sheets. To
load this color cycle in place of the default one::

  import matplotlib.pyplot as plt
  plt.style.use('tableau-colorblind10')

.. _reference: https://matplotlib.org/gallery/style_sheets/style_sheets_reference.html


Support for numpy.datetime64
----------------------------

Matplotlib has supported `datetime.datetime` dates for a long time in
`matplotlib.dates`.  We
now support `numpy.datetime64` dates as well.  Anywhere that
`datetime.datetime` could be used, `numpy.datetime64` can be used.  eg::

  time = np.arange('2005-02-01', '2005-02-02', dtype='datetime64[h]')
  plt.plot(time)



Writing animations with Pillow
------------------------------
It is now possible to use Pillow as an animation writer.  Supported output
formats are currently gif (Pillow>=3.4) and webp (Pillow>=5.0).  Use e.g. as ::

   from __future__ import division

   from matplotlib import pyplot as plt
   from matplotlib.animation import FuncAnimation, PillowWriter

   fig, ax = plt.subplots()
   line, = plt.plot([0, 1])

   def animate(i):
      line.set_ydata([0, i / 20])
      return [line]

   anim = FuncAnimation(fig, animate, 20, blit=True)
   anim.save("movie.gif", writer=PillowWriter(fps=24))
   plt.show()


Slider UI widget can snap to discrete values
--------------------------------------------

The slider UI widget can take the optional argument *valstep*.  Doing so
forces the slider to take on only discrete values, starting from *valmin* and
counting up to *valmax* with steps of size *valstep*.

If *closedmax==True*, then the slider will snap to *valmax* as well.



``capstyle`` and ``joinstyle`` attributes added to `.Collection`
----------------------------------------------------------------

The `.Collection` class now has customizable ``capstyle`` and ``joinstyle``
attributes. This allows the user for example to set the ``capstyle`` of
errorbars.


*pad* kwarg added to ax.set_title
---------------------------------

The method `.Axes.set_title` now has a *pad* kwarg, that specifies the
distance from the top of an axes to where the title is drawn.  The units
of *pad* is points, and the default is the value of the (already-existing)
:rc:`axes.titlepad`.


Comparison of 2 colors in Matplotlib
------------------------------------

As the colors in Matplotlib can be specified with a wide variety of ways, the
`matplotlib.colors.same_color` method has been added which checks if
two `~matplotlib.colors` are the same.


Autoscaling a polar plot snaps to the origin
--------------------------------------------

Setting the limits automatically in a polar plot now snaps the radial limit
to zero if the automatic limit is nearby. This means plotting from zero doesn't
automatically scale to include small negative values on the radial axis.

The limits can still be set manually in the usual way using `~.Axes.set_ylim`.


PathLike support
----------------

On Python 3.6+, `~matplotlib.pyplot.savefig`, `~matplotlib.pyplot.imsave`,
`~matplotlib.pyplot.imread`, and animation writers now accept `os.PathLike`\s
as input.


`.Axes.tick_params` can set gridline properties
-----------------------------------------------

`.Tick` objects hold gridlines as well as the tick mark and its label.
`.Axis.set_tick_params`, `.Axes.tick_params` and `.pyplot.tick_params`
now have keyword arguments 'grid_color', 'grid_alpha', 'grid_linewidth',
and 'grid_linestyle' for overriding the defaults in `.rcParams`:
'grid.color', etc.


`.Axes.imshow` clips RGB values to the valid range
--------------------------------------------------

When `.Axes.imshow` is passed an RGB or RGBA value with out-of-range
values, it now logs a warning and clips them to the valid range.
The old behaviour, wrapping back in to the range, often hid outliers
and made interpreting RGB images unreliable.


Properties in :file:`matplotlibrc` to place xaxis and yaxis tick labels
-----------------------------------------------------------------------

Introducing four new boolean properties in :file:`matplotlibrc` for default
positions of xaxis and yaxis tick labels, namely,
:rc:`xtick.labeltop`, :rc:`xtick.labelbottom`, :rc:`ytick.labelright` and
:rc:`ytick.labelleft`. These can also be changed in rcParams.


PGI bindings for gtk3
---------------------

The GTK3 backends can now use PGI_ instead of PyGObject_.  PGI is a fairly
incomplete binding for GObject, thus its use is not recommended; its main
benefit is its availability on Travis (thus allowing CI testing for the gtk3agg
and gtk3cairo backends).

The binding selection rules are as follows:
- if ``gi`` has already been imported, use it; else
- if ``pgi`` has already been imported, use it; else
- if ``gi`` can be imported, use it; else
- if ``pgi`` can be imported, use it; else
- error out.

Thus, to force usage of PGI when both bindings are installed, import it first.

.. _PGI: https://pgi.readthedocs.io/en/latest/
.. _PyGObject: https://pygobject.readthedocs.io/en/latest/



Cairo rendering for Qt, WX, and Tk canvases
-------------------------------------------

The new ``Qt4Cairo``, ``Qt5Cairo``, ``WXCairo``, and ``TkCairo``
backends allow Qt, Wx, and Tk canvases to use Cairo rendering instead of
Agg.


Added support for QT in new ToolManager
---------------------------------------

Now it is possible to use the ToolManager with Qt5
For example::

  import matplotlib

  matplotlib.use('QT5AGG')
  matplotlib.rcParams['toolbar'] = 'toolmanager'
  import matplotlib.pyplot as plt

  plt.plot([1,2,3])
  plt.show()


Treat the new Tool classes experimental for now, the API will likely change and perhaps the rcParam as well

The main example :doc:`/gallery/user_interfaces/toolmanager_sgskip` shows more
details, just adjust the header to use QT instead of GTK3



TkAgg backend reworked to support PyPy
--------------------------------------

PyPy_ can now plot using the TkAgg backend, supported on PyPy 5.9
and greater (both PyPy for python 2.7 and PyPy for python 3.5).

.. _PyPy: https://www.pypy.org/



Python logging library used for debug output
--------------------------------------------

Matplotlib has in the past (sporadically) used an internal
verbose-output reporter.  This version converts those calls to using the
standard python `logging` library.

Support for the old `.rcParams` ``verbose.level`` and ``verbose.fileo`` is
dropped.

The command-line options ``--verbose-helpful`` and ``--verbose-debug`` are
still accepted, but deprecated.  They are now equivalent to setting
``logging.INFO`` and ``logging.DEBUG``.

The logger's root name is ``matplotlib`` and can be accessed from programs
as::

  import logging
  mlog = logging.getLogger('matplotlib')

Instructions for basic usage are in :ref:`troubleshooting-faq` and for
developers in :ref:`contributing`.

.. _logging: https://docs.python.org/3/library/logging.html

Improved `repr` for `.Transform`\s
----------------------------------

`.Transform`\s now indent their `repr`\s in a more legible manner:

.. code-block:: ipython

   In [1]: l, = plt.plot([]); l.get_transform()
   Out[1]:
   CompositeGenericTransform(
      TransformWrapper(
         BlendedAffine2D(
               IdentityTransform(),
               IdentityTransform())),
      CompositeGenericTransform(
         BboxTransformFrom(
               TransformedBbox(
                  Bbox(x0=-0.05500000000000001, y0=-0.05500000000000001, x1=0.05500000000000001, y1=0.05500000000000001),
                  TransformWrapper(
                     BlendedAffine2D(
                           IdentityTransform(),
                           IdentityTransform())))),
         BboxTransformTo(
               TransformedBbox(
                  Bbox(x0=0.125, y0=0.10999999999999999, x1=0.9, y1=0.88),
                  BboxTransformTo(
                     TransformedBbox(
                           Bbox(x0=0.0, y0=0.0, x1=6.4, y1=4.8),
                           Affine2D(
                              [[ 100.    0.    0.]
                              [   0.  100.    0.]
                              [   0.    0.    1.]])))))))