Altair

https://github.com/vega/vega-lite/releases/tag/v4.0.0.

It is the first version of Altair to drop Python 2 compatibility, and is tested
on Python 3.5 and newer.

Enhancements

- Support for interactive legends: ([Example](http://altair-viz.github.io/gallery/interactive_legend.html#gallery-interactive-legend))
<img height="200" alt="interactive legend" src="https://user-images.githubusercontent.com/781659/70592444-aec9fb00-1b8e-11ea-8bf7-199a16810e0d.gif">

- Responsive chart width and height: ([Example](http://altair-viz.github.io/user_guide/customization.html#customization-chart-size))
<img height="200" alt="dynamic width" src="https://user-images.githubusercontent.com/781659/70593197-f782b380-1b90-11ea-8dcf-29282ea913b0.gif">

- Bins responsive to selections: ([Example](http://altair-viz.github.io/gallery/histogram_responsive.html#gallery-histogram-responsive))
<img height="200" alt="responsive bin" src="https://user-images.githubusercontent.com/781659/70596199-19346880-1b9a-11ea-9dec-f9739c2b055a.gif">

- New pivot transform: ([Example](http://altair-viz.github.io/user_guide/transform/pivot.html#user-guide-pivot-transform))
<img height="200" alt="pivot" src="https://user-images.githubusercontent.com/781659/70593369-a4f5c700-1b91-11ea-8655-9af0fbb3c149.gif">

- New Regression transform: ([Example](http://altair-viz.github.io/user_guide/transform/regression.html#user-guide-regression-transform))
<img height="200" alt="regression" src="https://user-images.githubusercontent.com/781659/70592667-78d94680-1b8f-11ea-999e-4b37725793a8.png">

- New LOESS transform: ([Example](http://altair-viz.github.io/user_guide/transform/loess.html#user-guide-loess-transform))
<img height="200" alt="loess" src="https://user-images.githubusercontent.com/781659/70592674-80005480-1b8f-11ea-99bf-9a36d5a50bd3.png">

- New density transform: ([Example](http://altair-viz.github.io/user_guide/transform/density.html#user-guide-density-transform))
<img height="200" alt="density" src="https://user-images.githubusercontent.com/781659/70592687-87bff900-1b8f-11ea-842b-0a68f666e26b.png">

- Image mark ([Example](http://altair-viz.github.io/user_guide/marks.html#image-mark))
<img height="200" alt="image" src="https://user-images.githubusercontent.com/781659/70592972-4b40cd00-1b90-11ea-93ca-81d49c196053.png">


- New default ``html`` renderer, directly compatible with Jupyter Notebook and
JupyterLab without the need for frontend extensions, as well as tools like
nbviewer and nbconvert, and related notebook environments such as Zeppelin,
Colab, Kaggle Kernels, and DataBricks. To enable the old default renderer, use:

alt.renderers.enable('mimetype')


- Support per-corner radius for bar marks: ([Example](http://altair-viz.github.io/gallery/bar_rounded.html#gallery-bar-rounded))
<img height="300" alt="round-bar" src="https://user-images.githubusercontent.com/781659/70592714-99090580-1b8f-11ea-9304-03d3967d600c.png">

Grammar Changes
- Sort-by-field can now use the encoding name directly. So instead of

alt.Y('y:Q', sort=alt.EncodingSortField('x_field', order='descending'))

you can now use::

alt.Y('y:Q', sort="-x")


- The ``rangeStep`` argument to :class:`Scale` and :meth:`Chart.configure_scale` is deprecated.
instead, use ``chart.properties(width={"step": rangeStep})`` or
``chart.configure_view(step=rangeStep)``.

- ``align``, ``center``, ``spacing``, and ``columns`` are no longer valid chart properties, but
are moved to the encoding classes to which they refer.

*released Nov 27, 2019*

Last release to support Python 2

Enhancements

- Add inheritance structure to low-level schema classes (1803)
- Add ``html`` renderer which works across frontends (1793)
- Support Python 3.8 (1740, 1781)
- Add ``:G`` shorthand for geojson type (1714)
- Add data generator interface: ``alt.sequence``, ``alt.graticule``,
``alt.sphere()`` (1667, 1687)
- Support geographic data sources via ``__geo_interface__`` (1664)

Bug Fixes

- Support ``pickle`` and ``copy.deepcopy`` for chart objects (1805)
- Fix bug when specifying ``count()`` within ``transform_joinaggregate()`` (1751)
- Fix ``LayerChart.add_selection`` (1794)
- Fix arguments to ``project()`` method (1717)
- Fix composition of multiple selections (1707)

Upgraded to Vega-Lite version 3.4 (See [Vega-Lite 3.4 Release Notes](https://github.com/vega/vega-lite/releases/tag/v3.4.0)).

Following are changes to Altair in addition to those that came with VL 3.4:

Enhancements

- Selector values can be used directly in expressions (1599)
- Top-level chart repr is now truncated to improve readability of error
messages (1572)

Bug Fixes

- top-level ``add_selection`` methods now delegate to sub-charts. Previously
they produced invalid charts (1607)
- Unsupported ``mark_*()`` methods removed from LayerChart (1607)
- New encoding channels are properly parsed (1597)
- Data context is propagated when encodings are specified as lists (1587)

Backward-Incompatible Changes
- ``alt.LayerChart`` no longer has ``mark_*()`` methods, because they never
produced valid chart specifications) (1607)

Update includes full compatibility with version 3.3 of Vega-Lite.

Enhancements

- Added support for [vega themes](https://github.com/vega/vega-themes) via `alt.themes.enable(theme_name)` (#1539)

- Added an `alt.renderers.disable_max_rows()` method for disabling the maximum rows check (1538)

- Improved user-facing warnings/errors around layering and faceting (1535).

- `data` argument is now properly handled by `Chart.properties` (1525)

- Compound charts (layer, concat, hconcat, vconcat) now move data to the top level by default. In particular, this means that the `facet()` method can now be called directly on a layered chart without having to change how data is specified. (1521)

- `alt.LayerChart` now supports `mark_*()` methods. If a layer specifies a mark at the top level, all child charts will inherit it (unless they override it explicitly).

- `alt.Chart.facet()` now handles wrapped facets; for example: `chart.facet('column_name', columns=5)` See `altair/examples/us_population_over_time_facet.py` for a more complete example.

Bug fixes

- Make `chart.serve()` and `chart.save()` respect the data transformer setting (1538)

- Fixed a deserialization bug for certain chart specs in schemapi (1543)

Backward-Incompatible Changes

- `alt.Chart.facet()` now accepts a wrapped facet encoding as a first positional argument, rather than a row encoding. The following are examples of old invocations, and the equivalent new invocations:

- `chart.facet(row='col1', column='col2')`: unchanged
- `chart.facet('col1', 'col2')`: change to `chart.facet(row='col1', column='col2')`
- `chart.facet('col1')`: change to `chart.facet(row='col1')`

In each case, the new invocations are compatible back to Altair 2.X.

- Several of the encoding channels added in 3.0 have had their capitalization corrected to better match the names used in the schema:

- `alt.Fillopacity` -> `alt.FillOpacity`
- `alt.Strokeopacity` -> `alt.StrokeOpacity`
- `alt.Strokewidth` -> `alt.StrokeWidth`
- `alt.Xerror` -> `alt.XError`
- `alt.Xerror2` -> `alt.XError2`
- `alt.Yerror` -> `alt.YError`
- `alt.Yerror2` -> `alt.YError2`

Fix version info bug for HTML output and Colab & Kaggle renderers.

Update to Vega-Lite 3.2 and Vega 5.3 & support all new features. See
https://github.com/vega/vega-lite/releases/tag/v3.0.0 for Vega-Lite
feature lists.

Highlights

- new compound marks: `mark_boxplot()`, `mark_errorband()`, `mark_errorbar()`
- new transforms: `transform_impute()`, `transform_joinaggregate()`, `transform_flatten()` `transform_fold()`, `transform_sample()`, `transform_stack()`
- new `facet` encoding that is similar to the `row` and `column` encoding, but allows for wrapped facets
- new `alt.concat()` function that is similar to `alt.hconcat` and `alt.vconcat`, but allows for more general wrapped concatenation
- new `columns` keyword that allows wrapped faceting, repeating, and concatenation.
- many, many bug fixes
- tooltips can now be automatically populated using the `tooltip` mark configuration.
- ability to specify initial conditions for selections