added new upgrade guide

[jameslbray]

Description of the issue/feature this PR addresses

Linked issue: #2644

Added a new upgrade guide to Python 3 and Plone 5 (P8).

I confirm I have tested this PR thoroughly and coded it according to PEP8
and Plone's Python styleguide standards.

[ramonski]

Hi @jameslbray,

many thanks for working out this upgrade guide and sharing some best practices to achieve Python 3 compatibility for SENAITE!

Maybe worth to mention that we are already on Plone 5.2.15 and not Plone 4 anymore.

While the guide contains many aspects that are worth following, I see many points that are simply not practical and therefore are not followed by developers or discourage them from contributing.

I like to keep it simple here and don't overcomplicate things.

Therefore, the most important step currently is to migrate existing AT contents to Dexterity while keeping backwards compatibility for our existing customers, as we do not want to loose anyone on our way to a Python 3 compatible SENAITE version.

Code audits, documentation, testing, etc. are performed during this phase and make not really sense to be performed as separate tasks or as a prerequisite to proceeding.

Hence, I would wish to have more a supporting hands-on guide for developers with best practices to follow and tools to use while in the code instead of a large document outlining a sequential process that might work for sure in a company with a full-time development department, but not really for Open Source projects.

Final words:

As long as we do progress, I see no reason to change the current strategy/procedure in our Python 3 migration plan or communicate anything we (or at least I) do not really do to others.

Comments are welcome as I might be also completely wrong with my views...

[xispa]

Fully agree with @ramonski

[jameslbray]

Hi @ramonski ,
Thank you so much for replying! I understand development within an Open Source project is different from a full development team and could have considered that more. I'm assuming AT is Archetypes which needs to be migrated to Dexterity since AT isn't compatible with Python3. I'll work to create a more supportive hands-on guide rather than a sequential process as outlined in the first draft of the guide.

For my information, I see Plone 6 is the most modern version of it available, so would the primary focus be on getting Python3 compatibility and backwards compatibility first?

This is my first contribution to an Open Source project and would love to continue helping the project. Let me know your thoughts/other inputs while I rewrite what I've got so far.