HEP 1 - Python Version Support#

Identifier HEP 1
Title Python Version Support
Status Accepted
Author(s) Ian Thomas
Created April 19, 2023
Accepted May 23, 2023
Last Updated March 15, 2024
Discussion https://github.com/holoviz/holoviz/pull/362
Implementation NA

Note: HEP 1 was updated on March 15, 2024 by Demetris Roumis to align with the updated HEP format, proposed by HEP 0. Notably, he added the table above and the ‘Resolution’ section below. If there is any discrepency between the reformatted HEP 1 and the original HEP 1, the original HEP 1 takes precedence.

Summary#

This enhancement proposal describes the possible policy that HoloViz projects might adopt for support of Python versions.

Resolution#

The community decided to adopt a Python version support policy for HoloViz projects that aims to support as many active Python releases as reasonably possible, with specific policies tailored for projects with few dependencies, those tightly coupled to Bokeh, and those with geospatial dependencies, ensuring alignment with dependent libraries’ support cycles.

Background#

Historically a new version of Python has been released every one to two years, and in future annual releases are planned every October. The lifespan of each version is typically five years, so on any particular date there are expected to be five active Python versions. The current status of Python versions is illustrated in the Python Developer’s Guide.

NumPy have a more restrictive policy of supporting Python version released in the last 42 months (three and a half years), with a few extra caveats, in NEP29. They therefore support the latest three to four Python releases.

A number of projects in the scientific Python ecosystem follow the NumPy policy including

Bokeh, a library of particular importance to HoloViz, has a policy to support at least the latest three versions of Python so although it does not explicitly follow NumPy’s policy it is similar.

At the time of writing in mid April 2023, Python versions currently supported are 3.7 to 3.11. 3.7 reaches end of life at the end of June, and Python 3.12 will be released in October. NumPy’s previous release (1.24.2) supported Python 3.8 to 3.11 and the next release will support 3.9 to 3.11. Bokeh’s most recent release (3.1.0) supported Python 3.8 to 3.11, and the next release (3.2.0) will support Python 3.9 to 3.11.

Specification/Policy#

Ideally HoloViz projects should support as many Python releases as are reasonably possible. Support for a new Python release should ideally occur on the day of release, but the limiting factor here is often numba as that is usually delayed.

Support for old versions of Python is limited, in a practical sense, by dependent libraries’ support for old versions. Dependencies that have a slow change cadence are usually not a problem, but those with a fast change cadence (e.g. pyarrow) or with major backward-breaking changes (e.g. Bokeh 3.0, pandas 2.0) potentially are. A desire to support older versions of Python here can result in HoloViz projects effectively performing the integration testing, fixes and workarounds for those dependencies that have already dropped support for older Python.

In deciding on a policy for support of old Python releases, the HoloViz projects can be divided into three groups:

  1. Colorcet and Param: projects with few dependencies.

  2. Panel, Lumen, HoloViews, hvPlot and Datashader: Panel is tightly coupled to Bokeh, and the other projects here are commonly used in Panel so they should also be considered tightly coupled to Bokeh.

  3. GeoViews and SpatialPandas: projects with geospatial dependencies (install or CI).

For 1, the limited dependencies means that support can be for all Python releases that are currently active.

For 2, the tight coupling with Bokeh means that Bokeh’s policy should be followed. However, this can be relaxed slightly so that following a Bokeh release that drops support for a particular Python version each of the HoloViz projects will make one further release supporting that Python version before dropping it themselves.

For 3 the geospatial dependencies often cause problems by not being available as wheels on PyPI and being difficult to resolve on conda. The HoloViz policy should be the same as that of 2 above for uniformity.

Illustration#

To illustrate the proposed policy, this is what it means for the remainder of 2023.

All projects currently support Python 3.11 and will support Python 3.12 when it is released in October or as soon as possible after that.

Colorcet and Param currently support Python 3.7 upwards. When this reaches end of life at the end of June, the minimum support Python version will increase to 3.8 for their next releases.

The current Bokeh release (3.1.0) supports minimum Python of 3.8 and the next release (3.2.0) will support minimum Python 3.9. All HoloViz projects (except Colorcet and Param which are covered above) should drop support for Python 3.7 as soon as possible to support a minimum Python of 3.8. Following release of Bokeh 3.2.0 there should be one further release per HoloViz project that supports Python.

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