ci: Moved vl-convert-python to save dependency group (vega#3609)

* Moved `vl-convert-python` to `save` dependency group

* Added `altair[save]` to installation.rst

* Update saving_charts.rst

* Update installation.rst

* Update saving_charts.rst

---------

Co-authored-by: Mattijn van Hoek <[email protected]>

doc/getting_started/installation.rst

@@ -24,6 +24,12 @@ and non-notebook IDEs, see :ref:`displaying-charts`.
 If you wish to install Altair with only the required dependencies,
 you can omit the ``[all]``/``-all`` suffix.
 
+Altair can also be installed with just the dependencies necessary for saving charts to offline HTML files or PNG/SVG/PDF formats, using:
+
+.. code-block:: bash
+
+    pip install "altair[save]"
+
 Development Installation
 ========================
 

doc/user_guide/saving_charts.rst

@@ -157,7 +157,7 @@ As an alternative, the ``inline=True`` keyword argument may be provided to ``cha
 
 .. note::
 
-   Calling ``chart.save`` with ``inline=True`` requires the :ref:`install-vl-convert` package.
+   Calling ``chart.save`` with ``inline=True`` requires :ref:`additional-dependencies`.
 
 
 .. _saving-png:
@@ -172,25 +172,11 @@ To save an Altair chart object as a PNG, SVG, or PDF image, you can use
     chart.save('chart.svg')
     chart.save('chart.pdf')
 
-Saving these images requires an additional extension vl-convert_ to run the
-javascript code necessary to interpret the Vega-Lite specification and output
-it in the form of an image.
-
-.. _install-vl-convert:
-
-vl-convert
-^^^^^^^^^^
-The vl-convert_ package can be installed with::
-
-    conda install -c conda-forge vl-convert-python
-
-or::
+.. note::
 
-    pip install vl-convert-python
+   :ref:`additional-dependencies` are required to save charts as images by running the javascript
+   code necessary to interpret the Vega-Lite specification and output it in the form of an image.
 
-vl-convert_ does not require any external dependencies.
-See the vl-convert documentation for information and for known
-`limitations <https://github.com/vega/vl-convert#limitations>`_.
 
 altair_saver
 ^^^^^^^^^^^^
@@ -216,6 +202,22 @@ size at the default resolution of 72 ppi::
 
     chart.save('chart.png', scale_factor=2)
 
+.. _additional-dependencies:
+
+Additional Dependencies
+~~~~~~~~~~~~~~~~~~~~~~~
+Saving charts to images or offline HTML files requires the vl-convert_ package::
+
+    conda install -c conda-forge vl-convert-python
+
+or::
+
+    pip install vl-convert-python
+
+vl-convert_ does not require any external dependencies.
+See the vl-convert documentation for information and for known
+`limitations <https://github.com/vega/vl-convert#limitations>`_.
+
 Sharable URL
 ~~~~~~~~~~~~
 The :meth:`Chart.to_url` method can be used to build a sharable URL that opens the chart
@@ -237,4 +239,4 @@ specification in the online Vega editor_.
 
 .. _vl-convert: https://github.com/vega/vl-convert
 .. _vegaEmbed: https://github.com/vega/vega-embed
-.. _editor: https://vega.github.io/editor/
+.. _editor: https://vega.github.io/editor/

pyproject.toml

@@ -53,9 +53,12 @@ Documentation = "https://altair-viz.github.io"
 Source = "https://github.com/vega/altair"
 
 [project.optional-dependencies]
+save = [
+    "vl-convert-python>=1.7.0",
+]
 all = [
+    "altair[save]",
     "vega_datasets>=0.9.0",
-    "vl-convert-python>=1.7.0",
     "pandas>=1.1.3",
     "numpy",
     "pyarrow>=11",