Public transform

[jannikluhn]

I'm trying to build a datastructure which internally uses a PVector but adds some functionality. I would like it to expose (almost) the same interface as a PVector. For most methods this is trivial (just a little verbose): I can call the corresponding method on my internal PVector and add my custom code. The only problem is transform: It seems like using pyrsistent._transformations.transform should just work, but I have two concerns:

• transform is technically not public
• it is unclear to me what the exact interface is that MyPVector and the corresponding evolver have to support to be compatible with transform

So my questions are:

• Can I rely on transform being stable? Is there a reason why it's not imported into the main namespace (if not I'd gladly create a PR)?

• By reading the code, transform seems to use

  • MyPVector.items or MyPVector.__iter__
  • MyPVector.__getitem__
  • MyPVector.evolver
  • MyEvolver.__delitem__
  • MyEvolver.__setitem__
  • MyEvolver.persistent()

  Have I missed anything?

[tobgu]

The reason transform is not public is exactly the things you mention above. It makes alot of assumptions about things that should be present and work in a particular way on a "transformable" object.

The internals of transform has been very stable for many years and I don't expect them to change in the near future. There are a couple of feature requests related to transform (#53, #89, #95) that could perhaps alter the behaviour. Most of them have been open for a long time though without anyone acting on them. I personally don't have time or interest to work on them ATM.

If I were in your spot I'd probably make use of the non-public function and make sure I had sufficient test coverage for the behaviour I want to support to notice any changes in the behaviour of transform. As stated above I expect it to be very stable but you never know... I don't think I'd like to commit to the exact interface required to support transforms at this time but perhaps it's not such a big deal. I've never really though about transform that way before.

[jannikluhn]

Fair enough, this sounds reasonable to me. Thank you for the assessment.