Import `TRANSCODING_SEPARATOR` to pipeline to make Kedro backwards compatible with `kedro-viz` on python 3.8

[ankatiyar]

Description

Flagged by e2e test on kedro-docker this morning (but not related to kedro-docker) - https://github.com/kedro-org/kedro-plugins/actions/runs/8730295535/job/23953858295#step:8:1

Context

• kedro-viz dropped support for python 3.8 in v.8.0.0
• we recently moved TRANSCODING_SEPARATOR to kedro.pipeline._transcoding.py from kedro.pipeline.pipeline.py
• This variable is used by kedro-viz in https://github.com/kedro-org/kedro-viz/blob/main/package/kedro_viz/integrations/kedro/hooks.py
  • they did update the import statement to work with older versions of Kedro so Kedro-Viz remains backwards compatible.

The problem

For python versions > 3.8, everything is okay ✅

For python version == 3.8: If a user has a project that uses both Kedro and Viz, the project becomes completely unusable -

• The last version of viz that supports python 3.8 is 7.1.0
• Kedro still supports python 3.8, so if a user creates a new project with 0.19.4 or upgrades the project to 0.19.4 it becomes a problem:

  ImportError: cannot import name 'TRANSCODING_SEPARATOR' from 
    'kedro.pipeline.pipeline' 
    (/usr/local/lib/python3.8/site-packages/kedro/pipeline/pipeline.py)

• User is then restricted to kedro versions < 0.19.4

Development notes

Proposed Solution 1

• Do nothing, it's a very small subset of users (python == 3.8, kedro == 0.19.4 and using kedro-viz for their projects)
• Issue a statement that you can't update to kedro 0.19.4 if you're on python 3.8 AND want to use kedro-viz (Uninstalling viz solves the problem)
• Additionally -
  • We can fix this in 0.19.5 but don't need to do an immediate patch release

Proposed Solution 2

• Add an import statement for TRANSCODE_SEPARATOR to kedro.pipeline.pipeline
• Do a patch release to make Kedro backwards compatible with kedro-viz

Other considerations (Bigger discussion)

• arrive at a consensus about which python versions should be supported by all Kedro/Viz/Plugins

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Checklist

• [ ] Read the contributing guidelines
• [ ] Signed off each commit with a Developer Certificate of Origin (DCO)
• [ ] Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• [ ] Updated the documentation to reflect the code changes
• [ ] Added a description of this change in the RELEASE.md file
• [ ] Added tests to cover my changes
• [ ] Checked if this change will affect Kedro-Viz, and if so, communicated that with the Viz team

[deepyaman]

Proposed Solution 2

• Add an import statement for TRANSCODE_SEPARATOR to kedro.pipeline.pipeline
• Do a patch release to make Kedro backwards compatible with kedro-viz

How about this, but just get rid of the _transcoding module and put the stuff back into pipeline. TBH I think adding the _transcoding module wasn't really necessary, and it introduced a new convention that doesn't exist anywhere else in the codebase (modules beginning with _).

But generally in favor of doing a patch release; easy fix that will avoid more questions, and show responsiveness.

[deepyaman]

Proposed Solution 2

• Add an import statement for TRANSCODE_SEPARATOR to kedro.pipeline.pipeline
• Do a patch release to make Kedro backwards compatible with kedro-viz

How about this, but just get rid of the _transcoding module and put the stuff back into pipeline. TBH I think adding the _transcoding module wasn't really necessary, and it introduced a new convention that doesn't exist anywhere else in the codebase (modules beginning with _).

But generally in favor of doing a patch release; easy fix that will avoid more questions, and show responsiveness.

To add some context to my suggestion—what was the original reason for moving stuff to the _transcoding module? The only somewhat functional thing I can see this does is make TRANSCODING_SEPARATOR not public (not totally sure why this is done; I have leveraged it in plugin code previously). However, if it was intentional to make this "private", then just importing it in pipeline undoes this, too.

[noklam]

we recently moved TRANSCODING_SEPARATOR to kedro.pipeline._transcoding.py from kedro.pipeline.pipeline.py

This is a breaking change and shouldn't be done in non-breaking release, we can do this but add a pointer to import from the new module instead. Agree with @deepyaman as I am not sure why this refactoring is necessary. It's not a big problem so a patch fix will do.

[merelcht]

To add some context to my suggestion—what was the original reason for moving stuff to the _transcoding module? The only somewhat functional thing I can see this does is make TRANSCODING_SEPARATOR not public (not totally sure why this is done; I have leveraged it in plugin code previously). However, if it was intentional to make this "private", then just importing it in pipeline undoes this, too.

It was done as part of https://github.com/kedro-org/kedro/pull/3812 to fix the issue with node dependencies uncovered by using the built-in toposort functionality. When reviewing it I didn't realise the transcoding separator was used outside of the framework and didn't think it was such a consequential refactor 😕

[ElenaKhaustova]

We missed that when we applied #3812 😔

Given the fact that the starters' tests will keep failing until we fix that, I would go with option 2 if it's relatively fast.

[deepyaman]

Approved with a small comment to explains why this is needed and remind ourselves this can be removed in 0.20

I think this actually shouldn't be removed in 0.20? By adding this, we're once again signaling that TRANSCODING_SEPARATOR is a public attribute that people can depend upon. Furthermore, my opinion is, TRANSCODING_SEPARATOR is something that should be exposed (it's not an internal-only implementation detail, and plugins use it, e.g. for catalog parsing).

[idanov]

@deepyaman The addition of the module is actually necessary, because it resolves a circular dependency between node.py and pipeline.py. So not really just random move, but a necessity. The convention of private modules is not unheard of, that's the same general convention for private elements in Python, but applied for modules, which is simply not as common, but still part of the convention.

[deepyaman]

@deepyaman The addition of the module is actually necessary, because it resolves a circular dependency between node.py and pipeline.py. So not really just random move, but a necessity.

There are other ways to remove circular dependencies, like not importing at the top level. It's not necessarily required. But that's fine.

The convention of private modules is not unheard of, that's the same general convention for private elements in Python, but applied for modules, which is simply not as common, but still part of the convention.

Yes, there are a lot of libraries that use it very heavily. My point is that Kedro does not use it anywhere—I searched before making that comment—so it's introducing a new convention in the codebase. Even naming it transcoding instead of _transcoding would be more consistent IMO.

[deepyaman]

@deepyaman The addition of the module is actually necessary, because it resolves a circular dependency between node.py and pipeline.py. So not really just random move, but a necessity.

There are other ways to remove circular dependencies, like not importing at the top level. It's not necessarily required.

Created a simple PR to illustrate: https://github.com/kedro-org/kedro/pull/3826