Switching backends via `matplotlib.use` is now allowed by default,
regardless of whether `matplotlib.pyplot` has been imported. If the user
tries to switch from an already-started interactive backend to a different
interactive backend, an `ImportError` will be raised.

Invalid points in PathCollections

The alpha-channel of RBGA images is now re-sampled independently of
RGB channels.  While this is a bug fix, it does change the output and
may result in some down-stream image comparison tests to fail.

Autoscaling
~~~~~~~~~~~
On log-axes where a single value is plotted at a "full" decade (1, 10, 100,
etc.), the autoscaling now expands the axis symmetrically around that point,
instead of adding a decade only to the right.

Log-scaled axes
~~~~~~~~~~~~~~~
When the default `.LogLocator` would generate no ticks for an axis (e.g., an
axis with limits from 0.31 to 0.39) or only a single tick, it now instead falls
back on the linear `.AutoLocator` to pick reasonable tick positions.

`.Figure.add_subplot` with no arguments

`~.Axes.bxp` now respects :rc:`boxplot.boxprops.linewidth` even when
*patch_artist* is set.
Previously, when the *patch_artist* parameter was set, `~.Axes.bxp` would ignore
:rc:`boxplot.boxprops.linewidth`.  This was an oversight -- in particular,
`~.Axes.boxplot` did not ignore it.

Major/minor tick collisions

import numpy as np
import matplotlib.dates as mdates
import matplotlib.pyplot as plt

t = np.arange("2018-11-03", "2018-11-06", dtype="datetime64")
x = np.random.rand(len(t))

fig, ax = plt.subplots()
ax.plot(t, x)
ax.xaxis.set(
    major_locator=mdates.DayLocator(),
    major_formatter=mdates.DateFormatter("\n%a"),
    minor_locator=mdates.HourLocator((0, 6, 12, 18)),
    minor_formatter=mdates.DateFormatter("%H:%M"),
)
# disable removing overlapping locations
ax.xaxis.remove_overlapping_locs = False
plt.show()

Previously, if :rc:`text.usetex` was True, then constructing a `.TextPath` on
a non-mathtext string with ``usetex=False`` would rely on the mathtext parser
(but not on usetex support!) to parse the string.  The mathtext parser is not
invoked anymore, which may cause slight changes in glyph positioning.

get_window_extents

Previously, `.Sankey.add` would only accept a single string as the *labels*
argument if its length is equal to the number of flows, in which case it would
use one character of the string for each flow.

The behavior has been changed to match the documented one: when a single string
is passed, it is used to label all the flows.

`~.font_manager.FontManager` scores

Text alignment was previously incorrect, in particular for multiline text
objects with large descenders (i.e. subscripts) and rotated text.  These have
been fixed and made more consistent, but could make old code that has
compensated for this no longer have the correct alignment.

Upper case color strings

When bounds passed to `~.axes.Axes.set_xlim` are degenerate (i.e. the
lower and upper value are equal), the method used to "expand" the
bounds now matches the expansion behavior of autoscaling when the plot
contains a single x-value, and should in particular produce nicer
limits for non-linear scales.

`~.Axes.plot` format string parsing

The HTMLWriter constructor is more strict: it no longer normalizes unknown
values of *default_mode* to 'loop', but errors out instead.

AFM parsing

`.Artist.set` now normalizes keywords before sorting them. Previously it sorted
its keyword arguments in reverse alphabetical order (with a special-case to
put ``color`` at the end) before applying them.

It now normalizes aliases (and, as above, emits a warning on duplicate
properties) before doing the sorting (so ``c`` goes to the end too).

`.Axes.tick_params` argument checking

Input that consists of multiple empty lists will now return a list of histogram
values for each one of the lists. For example, an input of ``[[],[]]`` will
return 2 lists of histogram values. Previously, a single list was returned.

``backend_bases.TimerBase.remove_callback`` future signature change

`~.container.StemContainer` objects can now store a
`~.collections.LineCollection` object instead of a list of
`~.lines.Line2D` objects for stem lines plotted using
`~.Axes.stem`. This gives a very large performance boost to displaying
and moving `~.Axes.stem` plots.

This will become the default behaviour in Matplotlib 3.3. To use it
now, the *use_line_collection* keyword argument to `~.Axes.stem` can
be set to `True` ::

  ax.stem(..., use_line_collection=True)

Individual line segments can be extracted from the
`~.collections.LineCollection` using
`~.collections.LineCollection.get_segments()`. See the
`~.collections.LineCollection` documentation for other methods to
retrieve the collection properties.


`~matplotlib.colorbar.ColorbarBase` inheritance
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`matplotlib.colorbar.ColorbarBase` is no longer a subclass of
`.cm.ScalarMappable`.  This inheritance lead to a confusing situation
where the `.cm.ScalarMappable` passed to `matplotlib.colorbar.Colorbar`
(`~.Figure.colorbar`) had a ``set_norm`` method, as did the colorbar.
The colorbar is now purely a follower to the `.ScalarMappable` norm and
colormap, and the old inherited methods
``matplotlib.colorbar.ColorbarBase.set_norm``,
``matplotlib.colorbar.ColorbarBase.set_cmap``,
``matplotlib.colorbar.ColorbarBase.set_clim`` are deprecated, as are
the getter versions of those calls.  To set the norm associated with a
colorbar do ``colorbar.mappable.set_norm()`` etc.


FreeType and libpng search paths
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The ``MPLBASEDIRLIST`` environment variables and ``basedirlist`` entry in
``setup.cfg`` have no effect anymore.  Instead, if building in situations where
FreeType or libpng are not in the compiler or linker's default path, set the
standard environment variables ``CFLAGS``/``LDFLAGS`` on Linux or OSX, or
``CL``/``LINK`` on Windows, to indicate the relevant paths.

See details in :doc:`/install/index`.

Setting artist properties twice or more in the same call

Path code types like ``Path.MOVETO`` are now ``np.uint8`` instead of ``int``
``Path.STOP``, ``Path.MOVETO``, ``Path.LINETO``, ``Path.CURVE3``,
``Path.CURVE4`` and ``Path.CLOSEPOLY`` are now of the type ``Path.code_type``
(``np.uint8`` by default) instead of plain ``int``. This makes their type
match the array value type of the ``Path.codes`` array.

LaTeX code in matplotlibrc file

The method `.Axes.spy` now raises a `TypeError` for the keyword
arguments *interpolation* and *linestyle* instead of silently ignoring
them.

Furthermore, `.Axes.spy` spy does now allow for an *extent* argument
(was silently ignored so far).

A bug with ``Axes.spy(..., origin='lower')`` is fixed.  Previously this
flipped the data but not the y-axis resulting in a mismatch between
axes labels and actual data indices. Now, *origin='lower'* flips both
the data and the y-axis labels.

Boxplot tick methods

MouseEvents now include the event name in their ``str()``.
Previously they contained the prefix "MPL MouseEvent".

RGBA buffer return type

``matplotlib.font_manager.win32InstalledFonts`` returns an empty list instead
of None if no fonts are found.

``Axes.fmt_xdata`` and ``Axes.fmt_ydata`` error handling
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Previously, if the user provided a ``Axes.fmt_xdata`` or
``Axes.fmt_ydata`` function that raised a `TypeError` (or set them to a
non-callable), the exception would be silently ignored and the default
formatter be used instead.  This is no longer the case; the exception
is now propagated out.

Deprecation of redundant `.Tick` attributes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``gridOn``, ``tick1On``, ``tick2On``, ``label1On``, and ``label2On``
`~.Tick` attributes have been deprecated.  Directly get and set the visibility
on the underlying artists, available as the ``gridline``, ``tick1line``,
``tick2line``, ``label1``, and ``label2`` attributes.

The ``label`` attribute, which was an alias for ``label1``, has been
deprecated.

Subclasses that relied on setting the above visibility attributes needs to be
updated; see e.g. :file:`examples/api/skewt.py`.

Passing a Line2D's drawstyle together with the linestyle is deprecated

The following deprecated rcParams have been removed:

- ``text.dvipnghack``
- ``nbagg.transparent`` (use :rc:`figure.facecolor` instead)
- ``plugins.directory``
- ``axes.hold``
- ``backend.qt4`` and ``backend.qt5`` (set the :envvar:`QT_API` environment
  variable instead)

Deprecated

- ``Verbose`` (replaced by python logging library)
- ``artist.Artist.hitlist`` (no replacement)
- ``artist.Artist.is_figure_set`` (use ``artist.figure is not None`` instead)
- ``axis.Axis.unit_data`` (use ``axis.Axis.units`` instead)
- ``backend_bases.FigureCanvasBase.onRemove`` (no replacement)
  ``backend_bases.FigureManagerBase.show_popup`` (this never did anything)
- ``backend_wx.SubplotToolWx`` (no replacement)
- ``backend_wx.Toolbar`` (use ``backend_wx.NavigationToolbar2Wx`` instead)
- ``cbook.align_iterators`` (no replacement)
- ``contour.ContourLabeler.get_real_label_width`` (no replacement)
- ``legend.Legend.draggable`` (use `.legend.Legend.set_draggable()` instead)
- ``texmanager.TexManager.postscriptd``, ``texmanager.TexManager.pscnt``,
  ``texmanager.TexManager.make_ps``, ``texmanager.TexManager.get_ps_bbox``
  (no replacements)

Arguments
~~~~~~~~~
- The *fig* kwarg to `.GridSpec.get_subplot_params` and
  `.GridSpecFromSubplotSpec.get_subplot_params` (use the argument
  *figure* instead)
- Passing 'box-forced' to `.Axes.set_adjustable` (use 'box' instead)
- Support for the strings 'on'/'true'/'off'/'false' to mean
  `True` / `False` (directly use `True` / `False` instead).
  The following functions are affected:

  - `.axes.Axes.grid`
  - `.Axes3D.grid`
  - `.Axis.set_tick_params`
  - `.pyplot.box`
- Using `.pyplot.axes` with an `.axes.Axes` type argument
  (use `.pyplot.sca` instead)

Other
~~~~~
The following miscellaneous API elements have been removed

- svgfont support (in :rc:`svg.fonttype`)
- Logging is now done with the standard python ``logging`` library.
  ``matplotlib.verbose`` and the command line switches ``--verbose-LEVEL`` have
  been removed.

  To control the logging output use::

    import logging
    logger = logging.getLogger('matplotlib')
    logger.setLevel(logging.INFO)
    # configure log handling: Either include it into your ``logging`` hierarchy,
    # e.g. by configuring a root looger using ``logging.basicConfig()``,
    # or add a standalone handler to the matplotlib logger:
    logger.addHandler(logging.StreamHandler())

- ``__version__numpy__``
- ``collections.CIRCLE_AREA_FACTOR``
- ``font_manager.USE_FONTCONFIG``
- ``font_manager.cachedir``

:mod:`matplotlib.mlab` removals
-------------------------------
Lots of code inside the :mod:`matplotlib.mlab` module which was deprecated
in Matplotlib 2.2 has been removed. See below for a list:

- ``mlab.exp_safe`` (use `numpy.exp` instead)
- ``mlab.amap``
- ``mlab.logspace`` (use `numpy.logspace` instead)
- ``mlab.rms_flat``
- ``mlab.l1norm`` (use ``numpy.linalg.norm(a, ord=1)`` instead)
- ``mlab.l2norm`` (use ``numpy.linalg.norm(a, ord=2)`` instead)
- ``mlab.norm_flat`` (use ``numpy.linalg.norm(a.flat, ord=2)`` instead)
- ``mlab.frange`` (use `numpy.arange` instead)
- ``mlab.identity`` (use `numpy.identity` instead)
- ``mlab.base_repr``
- ``mlab.binary_repr``
- ``mlab.ispower2``
- ``mlab.log2`` (use `numpy.log2` instead)
- ``mlab.isvector``
- ``mlab.movavg``
- ``mlab.safe_isinf`` (use `numpy.isinf` instead)
- ``mlab.safe_isnan`` (use `numpy.isnan` instead)
- ``mlab.cohere_pairs`` (use `scipy.signal.coherence` instead)
- ``mlab.entropy`` (use `scipy.stats.entropy` instead)
- ``mlab.normpdf`` (use ``scipy.stats.norm.pdf`` instead)
- ``mlab.find`` (use ``np.nonzero(np.ravel(condition))`` instead)
- ``mlab.longest_contiguous_ones``
- ``mlab.longest_ones``
- ``mlab.PCA``
- ``mlab.prctile`` (use `numpy.percentile` instead)
- ``mlab.prctile_rank``
- ``mlab.center_matrix``
- ``mlab.rk4`` (use `scipy.integrate.ode` instead)
- ``mlab.bivariate_normal``
- ``mlab.get_xyz_where``
- ``mlab.get_sparse_matrix``
- ``mlab.dist`` (use `numpy.hypot` instead)
- ``mlab.dist_point_to_segment``
- ``mlab.griddata`` (use `scipy.interpolate.griddata`)
- ``mlab.less_simple_linear_interpolation`` (use `numpy.interp`)
- ``mlab.slopes``
- ``mlab.stineman_interp``
- ``mlab.segments_intersect``
- ``mlab.fftsurr``
- ``mlab.offset_line``
- ``mlab.quad2cubic``
- ``mlab.vector_lengths``
- ``mlab.distances_along_curve``
- ``mlab.path_length``
- ``mlab.cross_from_above``
- ``mlab.cross_from_below``
- ``mlab.contiguous_regions`` (use `.cbook.contiguous_regions` instead)
- ``mlab.is_closed_polygon``
- ``mlab.poly_between``
- ``mlab.poly_below``
- ``mlab.inside_poly``
- ``mlab.csv2rec``
- ``mlab.rec2csv`` (use `numpy.recarray.tofile` instead)
- ``mlab.rec2text`` (use `numpy.recarray.tofile` instead)
- ``mlab.rec_summarize``
- ``mlab.rec_join``
- ``mlab.recs_join``
- ``mlab.rec_groupby``
- ``mlab.rec_keep_fields``
- ``mlab.rec_drop_fields``
- ``mlab.rec_append_fields``
- ``mlab.csvformat_factory``
- ``mlab.get_formatd``
- ``mlab.FormatDatetime`` (use `datetime.datetime.strftime` instead)
- ``mlab.FormatDate`` (use `datetime.date.strftime` instead)
- ``mlab.FormatMillions``, ``mlab.FormatThousands``, ``mlab.FormatPercent``,
  ``mlab.FormatBool``, ``mlab.FormatInt``, ``mlab.FormatFloat``,
  ``mlab.FormatFormatStr``, ``mlab.FormatString``, ``mlab.FormatObj``
- ``mlab.donothing_callback``

`pylab` removals
----------------
Lots of code inside the :mod:`matplotlib.mlab` module which was deprecated
in Matplotlib 2.2 has been removed. This means the following functions are
no longer available in the `pylab` module:

- ``amap``
- ``base_repr``
- ``binary_repr``
- ``bivariate_normal``
- ``center_matrix``
- ``csv2rec`` (use `numpy.recarray.tofile` instead)
- ``dist`` (use `numpy.hypot` instead)
- ``dist_point_to_segment``
- ``distances_along_curve``
- ``entropy`` (use `scipy.stats.entropy` instead)
- ``exp_safe`` (use `numpy.exp` instead)
- ``fftsurr``
- ``find`` (use ``np.nonzero(np.ravel(condition))`` instead)
- ``frange`` (use `numpy.arange` instead)
- ``get_sparse_matrix``
- ``get_xyz_where``
- ``griddata`` (use `scipy.interpolate.griddata` instead)
- ``identity`` (use `numpy.identity` instead)
- ``inside_poly``
- ``is_closed_polygon``
- ``ispower2``
- ``isvector``
- ``l1norm`` (use ``numpy.linalg.norm(a, ord=1)`` instead)
- ``l2norm`` (use ``numpy.linalg.norm(a, ord=2)`` instead)
- ``log2`` (use `numpy.log2` instead)
- ``longest_contiguous_ones``
- ``longest_ones``
- ``movavg``
- ``norm_flat`` (use ``numpy.linalg.norm(a.flat, ord=2)`` instead)
- ``normpdf`` (use ``scipy.stats.norm.pdf`` instead)
- ``path_length``
- ``poly_below``
- ``poly_between``
- ``prctile`` (use `numpy.percentile` instead)
- ``prctile_rank``
- ``rec2csv`` (use `numpy.recarray.tofile` instead)
- ``rec_append_fields``
- ``rec_drop_fields``
- ``rec_join``
- ``rk4`` (use `scipy.integrate.ode` instead)
- ``rms_flat``
- ``segments_intersect``
- ``slopes``
- ``stineman_interp``
- ``vector_lengths``

mplot3d changes
---------------

Voxel shading
~~~~~~~~~~~~~
`.Axes3D.voxels` now shades the resulting voxels; for more details see
What's new. The previous behavior can be achieved by passing ::

  ax.voxels(.., shade=False)



Equal aspect axes disabled

`.Poly3DCollection.set_zsort` no longer silently ignores invalid
inputs, or `False` (which was always broken).  Passing `True` to mean
``"average"`` is deprecated.

Testing
-------
The ``--no-network`` flag to ``tests.py`` has been removed (no test requires
internet access anymore).  If it is desired to disable internet access both for
old and new versions of Matplotlib, use ``tests.py -m 'not network'`` (which is
now a no-op).

The image comparison test decorators now skip (rather than xfail) the test for
uncomparable formats. The affected decorators are `~.image_comparison` and
`~.check_figures_equal`. The deprecated ``ImageComparisonTest`` class is
likewise changed.

Dependency changes
------------------

NumPy
~~~~~
Matplotlib 3.1 now requires NumPy>=1.11.

ghostscript
~~~~~~~~~~~
Support for ghostscript 8.60 (released in 2007) has been removed.  The oldest
supported version of ghostscript is now 9.0 (released in 2010).

Mathtext changes
----------------
- In constructs such as ``"$1~2$"``, mathtext now interprets the tilde as a
  space, consistently with TeX (this was previously a parse error).

Deprecations
~~~~~~~~~~~~
- The ``\stackrel`` mathtext command has been deprecated (it behaved differently
  from LaTeX's ``\stackrel``.  To stack two mathtext expressions, use
  ``\genfrac{left-delim}{right-delim}{fraction-bar-thickness}{}{top}{bottom}``.
- The ``\mathcircled`` mathtext command (which is not a real TeX command)
  is deprecated.  Directly use unicode characters (e.g.
  ``"\N{CIRCLED LATIN CAPITAL LETTER A}"`` or ``"\u24b6"``) instead.
- Support for setting :rc:`mathtext.default` to circled is deprecated.

Signature deprecations
----------------------
The following signature related behaviours are deprecated:

- The *withdash* keyword argument to `.Axes.text()`. Consider using
  `.Axes.annotate()` instead.
- Passing (n, 1)-shaped error arrays to `.Axes.errorbar()`, which was not
  documented and did not work for ``n = 2``. Pass a 1D array instead.
- The *frameon* keyword argument to `~.Figure.savefig` and the ``savefig.frameon``
  rcParam. To emulate ``frameon = False``, set *facecolor* to fully
  transparent (``"none"``, or ``(0, 0, 0, 0)``).
- Passing a non-1D (typically, (n, 1)-shaped) input to `.Axes.pie`.
  Pass a 1D array instead.
- The `.TextPath` constructor used to silently drop ignored arguments; this
  behavior is deprecated.
- The *usetex* parameter of `.TextToPath.get_text_path` is deprecated and
  folded into the *ismath* parameter, which can now take the values
  `False`, `True`, and ``"TeX"``, consistently with other low-level
  text processing functions.
- Passing ``'normal'`` to `.axes.Axes.axis()` is deprecated, use
  ``ax.axis('auto')`` instead.
- Passing the *block* argument of `.pyplot.show` positionally is deprecated; it
  should be passed by keyword.
- When using the nbagg backend, `.pyplot.show` used to silently accept and ignore
  all combinations of positional and keyword arguments.  This behavior is
  deprecated.
- The unused *shape* and *imlim* parameters to `.Axes.imshow` are
  deprecated.  To avoid triggering the deprecation warning, the *filternorm*,
  *filterrad*, *resample*, and *url* arguments should be passed by
  keyword.
- The *interp_at_native* parameter to `.BboxImage`, which has had no effect
  since Matplotlib 2.0, is deprecated.
- All arguments to the ``matplotlib.cbook.deprecation.deprecated`` decorator
  and ``matplotlib.cbook.deprecation.warn_deprecated`` function, except the
  first one (the version where the deprecation occurred), are now keyword-only.
  The goal is to avoid accidentally setting the "message" argument when the
  "name" (or "alternative") argument was intended, as this has repeatedly
  occurred in the past.
- The arguments of `matplotlib.testing.compare.calculate_rms` have been renamed
  from ``expectedImage, actualImage``, to ``expected_image, actual_image``.
- Passing positional arguments to `.Axis.set_ticklabels` beyond *ticklabels*
  itself has no effect, and support for them is deprecated.
- Passing ``shade=None`` to `~.axes3d.Axes3D.plot_surface` is deprecated. This
  was an unintended implementation detail with the same semantics as
  ``shade=False``. Please use the latter code instead.
- `matplotlib.ticker.MaxNLocator` and its *set_params* method will issue
  a warning on unknown keyword arguments instead of silently ignoring them.
  Future versions will raise an error.

Changes in parameter names
--------------------------

- The *arg* parameter to `matplotlib.use` has been renamed to *backend*.

  This will only affect cases where that parameter has been set
  as a keyword argument. The common usage pattern as a positional argument
  ``matplotlib.use('Qt5Agg')`` is not affected.
- The *normed* parameter to `.Axes.hist2d` has been renamed to *density*.
- The *s* parameter to `.Annotation` (and indirectly `.Axes.annotate`) has
  been renamed to *text*.
- The *tolerence* parameter to
  `.bezier.find_bezier_t_intersecting_with_closedpath`,
  `.bezier.split_bezier_intersecting_with_closedpath`,
  ``bezier.find_r_to_boundary_of_closedpath``,
  `.bezier.split_path_inout` and `.bezier.check_if_parallel` has been renamed to
  *tolerance*.

In each case, the old parameter name remains supported (it cannot be used
simultaneously with the new name), but support for it will be dropped in
Matplotlib 3.3.

Class/method/attribute deprecations
-----------------------------------



Support for custom backends that do not provide a
`.GraphicsContextBase.set_hatch_color` method is deprecated.  We
suggest that custom backends let their ``GraphicsContext`` class
inherit from `.GraphicsContextBase`, to at least provide stubs for all
required methods.

- ``spine.Spine.is_frame_like``

This has not been used in the codebase since its addition in 2009.

- ``axis3d.Axis.get_tick_positions``

  This has never been used internally, there is no equivalent method exists on
  the 2D Axis classes, and despite the similar name, it has a completely
  different behavior from the 2D Axis' ``axis.Axis.get_ticks_position`` method.
- ``.backend_pgf.LatexManagerFactory``

- ``mpl_toolkits.axisartist.axislines.SimpleChainedObjects``
- ``mpl_toolkits.Axes.AxisDict``

Internal Helper Functions
~~~~~~~~~~~~~~~~~~~~~~~~~

- ``checkdep_dvipng``
- ``checkdep_ghostscript``
- ``checkdep_pdftops``
- ``checkdep_inkscape``


- ``ticker.decade_up``
- ``ticker.decade_down``


- ``cbook.dedent``
- ``docstring.Appender``
- ``docstring.dedent``
- ``docstring.copy_dedent``

Use the standard library's docstring manipulation tools instead, such as
`inspect.cleandoc` and `inspect.getdoc`.



- ``matplotlib.scale.get_scale_docs()``
- ``matplotlib.pyplot.get_scale_docs()``

These are considered internal and will be removed from the public API in a
future version.

- ``projections.process_projection_requirements``

- ``backend_ps.PsBackendHelper``
- ``backend_ps.ps_backend_helper``,

- ``cbook.iterable``
- ``cbook.get_label``
- ``cbook.safezip``
  Manually check the lengths of the inputs instead, or rely on NumPy to do it.
- ``cbook.is_hashable``
  Use ``isinstance(..., collections.abc.Hashable)`` instead.

- The ``.backend_bases.RendererBase.strip_math``.  Use
  `.cbook.strip_math` instead.

Multiple internal functions that were exposed as part of the public API
of `.mpl_toolkits.mplot3d` are deprecated,

**mpl_toolkits.mplot3d.art3d**

- ``mpl_toolkits.mplot3d.art3d.norm_angle``
- ``mpl_toolkits.mplot3d.art3d.norm_text_angle``
- ``mpl_toolkits.mplot3d.art3d.path_to_3d_segment``
- ``mpl_toolkits.mplot3d.art3d.paths_to_3d_segments``
- ``mpl_toolkits.mplot3d.art3d.path_to_3d_segment_with_codes``
- ``mpl_toolkits.mplot3d.art3d.paths_to_3d_segments_with_codes``
- ``mpl_toolkits.mplot3d.art3d.get_patch_verts``
- ``mpl_toolkits.mplot3d.art3d.get_colors``
- ``mpl_toolkits.mplot3d.art3d.zalpha``

**mpl_toolkits.mplot3d.proj3d**

- ``mpl_toolkits.mplot3d.proj3d.line2d``
- ``mpl_toolkits.mplot3d.proj3d.line2d_dist``
- ``mpl_toolkits.mplot3d.proj3d.line2d_seg_dist``
- ``mpl_toolkits.mplot3d.proj3d.mod``
- ``mpl_toolkits.mplot3d.proj3d.proj_transform_vec``
- ``mpl_toolkits.mplot3d.proj3d.proj_transform_vec_clip``
- ``mpl_toolkits.mplot3d.proj3d.vec_pad_ones``
- ``mpl_toolkits.mplot3d.proj3d.proj_trans_clip_points``

If your project relies on these functions, consider vendoring them.


Font Handling
~~~~~~~~~~~~~

- ``backend_pdf.RendererPdf.afm_font_cache``
- ``backend_ps.RendererPS.afmfontd``
- ``font_manager.OSXInstalledFonts``
- ``.TextToPath.glyph_to_path`` (Instead call ``font.get_path()`` and manually
  transform the path.)


Date related functions
~~~~~~~~~~~~~~~~~~~~~~

- ``dates.seconds()``
- ``dates.minutes()``
- ``dates.hours()``
- ``dates.weeks()``
- ``dates.strpdate2num``
- ``dates.bytespdate2num``

These are brittle in the presence of locale changes.  Use standard datetime
parsers such as `time.strptime` or `dateutil.parser.parse`, and additionally
call `matplotlib.dates.date2num` if you need to convert to Matplotlib's
internal datetime representation; or use ``dates.datestr2num``.

Axes3D
~~~~~~

- ``.axes3d.Axes3D.w_xaxis``
- ``.axes3d.Axes3D.w_yaxis``
- ``.axes3d.Axes3D.w_zaxis``

Use ``axes3d.Axes3D.xaxis``, ``axes3d.Axes3D.yaxis`` and
``axes3d.Axes3D.zaxis`` instead.

Testing
~~~~~~~

- ``matplotlib.testing.decorators.switch_backend`` decorator

Test functions should use ``pytest.mark.backend``, and the mark will be
picked up by the ``matplotlib.testing.conftest.mpl_test_settings`` fixture.

Quiver
~~~~~~

- ``.color`` attribute of `.Quiver` objects

Instead, use (as for any `.Collection`) the ``get_facecolor`` method.
Note that setting to the ``.color`` attribute did not update the quiver artist,
whereas calling ``set_facecolor`` does.

GUI / backend details
~~~~~~~~~~~~~~~~~~~~~

- ``.get_py2exe_datafiles``
- ``.tk_window_focus``
- ``.backend_gtk3.FileChooserDialog``
- ``.backend_gtk3.NavigationToolbar2GTK3.get_filechooser``
- ``.backend_gtk3.SaveFigureGTK3.get_filechooser``
- ``.NavigationToolbar2QT.adj_window`` attribute. This is unused and always ``None``.
- ``.backend_wx.IDLE_DELAY`` global variable
  This is unused and only relevant to the now removed wx "idling" code (note that
  as it is a module-level global, no deprecation warning is emitted when
  accessing it).
- ``mlab.demean``
- ``backend_gtk3cairo.FigureCanvasGTK3Cairo``,
- ``backend_wx.debug_on_error``, ``backend_wx.fake_stderr``,
  ``backend_wx.raise_msg_to_str``, ``backend_wx.MenuButtonWx``,
  ``backend_wx.PrintoutWx``,
- ``matplotlib.backends.qt_editor.formlayout`` module

This module is a vendored, modified version of the official formlayout_ module
available on PyPI. Install that module separately if you need it.

.. _formlayout: https://pypi.org/project/formlayout/

- ``GraphicsContextPS.shouldstroke``


Transforms / scales
~~~~~~~~~~~~~~~~~~~

- ``LogTransformBase``
- ``Log10Transform``
- ``Log2Transform``,
- ``NaturalLogTransformLog``
- ``InvertedLogTransformBase``
- ``InvertedLog10Transform``
- ``InvertedLog2Transform``
- ``InvertedNaturalLogTransform``

These classes defined in :mod:`matplotlib.scale` are deprecated.
As a replacement, use the general `~.scale.LogTransform` and `~.scale.InvertedLogTransform`
classes, whose constructors take a *base* argument.

Locators / Formatters
~~~~~~~~~~~~~~~~~~~~~

- ``OldScalarFormatter.pprint_val``
- ``ScalarFormatter.pprint_val``
- ``LogFormatter.pprint_val``

These are helper methods that do not have a consistent signature across
formatter classes.

Path tools
~~~~~~~~~~

- ``path.get_paths_extents``

Use `~.path.get_path_collection_extents` instead.

- ``.Path.has_nonfinite`` attribute

Use ``not np.isfinite(path.vertices).all()`` instead.

- ``.bezier.find_r_to_boundary_of_closedpath`` function is deprecated

This has always returned None instead of the requested radius.

Text
~~~~

- ``text.TextWithDash``
- ``Text.is_math_text``
- ``TextPath.is_math_text``
- ``TextPath.text_get_vertices_codes`` (As an alternative, construct a new ``TextPath`` object.)

Unused attributes
~~~~~~~~~~~~~~~~~

- ``NavigationToolbar2QT.buttons``
- ``Line2D.verticalOffset``
- ``Quiver.keytext``
- ``Quiver.keyvec``
- ``SpanSelector.buttonDown``

These are unused and never updated.


Sphinx extensions
~~~~~~~~~~~~~~~~~

- ``matplotlib.sphinxext.mathmpl.math_directive``
- ``matplotlib.sphinxext.plot_directive.plot_directive``

This is because the ``matplotlib.sphinxext.mathmpl`` and
``matplotlib.sphinxext.plot_directive`` interfaces have changed from the
(Sphinx-)deprecated function-based interface to a class-based interface; this
should not affect end users.

- ``mpl_toolkits.axisartist.axis_artist.UnimplementedException``

Environmental Variables
~~~~~~~~~~~~~~~~~~~~~~~

- The ``MATPLOTLIBDATA`` environment variable


Axis
~~~~

- ``Axis.iter_ticks``

This only served as a helper to the private ``Axis._update_ticks``


Undeprecations
--------------
The following API elements have been un-deprecated:

- The *obj_type* keyword argument to the
  ``matplotlib.cbook.deprecation.deprecated`` decorator.
- *xmin*, *xmax* keyword arguments to `.Axes.set_xlim` and *ymin*, *ymax*
  keyword arguments to `.Axes.set_ylim`


New features
------------

`.Text` now has a ``c`` alias for the ``color`` property

It is now possible to go beyond the tenth color in the property cycle using
``Cn`` syntax, e.g. ::

  plt.plot([1, 2], color="C11")

now uses the 12th color in the cycle.

Note that previously, a construct such as::

  plt.plot([1, 2], "C11")

would be interpreted as a request to use color ``C1`` and marker ``1``
(an "inverted Y").  To obtain such a plot, one should now use ::

  plt.plot([1, 2], "1C1")

(so that the first "1" gets correctly interpreted as a marker
specification), or, more explicitly::

  plt.plot([1, 2], marker="1", color="C1")


New `.Formatter.format_ticks` method

pcolorfast now accepts 3D images (RGB or RGBA) arrays if the X and Y
specifications allow image or pcolorimage rendering; they remain unsupported by
the more general quadmesh rendering


Invalid inputs
--------------

Passing invalid locations to `~.Axes.legend` and `~.Axes.table` used
to fallback on a default location.  This behavior is deprecated and
will throw an exception in a future version.

`.offsetbox.AnchoredText` is unable to handle the *horizontalalignment* or
*verticalalignment* kwargs, and used to ignore them with a warning.  This
behavior is deprecated and will throw an exception in a future version.

Passing steps less than 1 or greater than 10 to `~.ticker.MaxNLocator` used to
result in undefined behavior.  It now throws a `ValueError`.

The signature of the (private) ``Axis._update_ticks`` has been changed to not
take the renderer as argument anymore (that argument is unused).