Make `PyObject` parametric?

Thinking about conversion between Julia and Python values and semantics, I wonder if we could make `PyObject` parametric, so make it `PyObject{P <: PyConversionPolicy}` where `P` encodes how we want to interpret the object.

For example, `PyObject{Nice}` would be equivalent to `PyObject` as it is now, with user-friendly automatic conversions. `PyObject{Raw}` would perform no automatic conversion at all, which would be useful for wrapping Python packages into Julia, where complete control is required. Other possibilities could be `PyObject{Numpy}` which converts Julia arrays to numpy arrays instead of to lists, for example.

This policy parameter would be inherited in a natural way, so operations on objects with the same policy produce an object with that policy.

I don't know if the effort to implement this would be worth it, since you can already achieve the same things using PyCall's clunkier syntax, but I just wanted to gather opinions and suggestions.

Commencez par lire le comportement de conversion existant de PyObject et la syntaxe de PyCall à laquelle l’issue le compare. Déterminez si une PyConversionPolicy avec les variantes Nice, Raw et Numpy est souhaitée, y compris l’héritage de la policy entre les opérations ; le travail serait terminé lorsqu’un accord aurait été trouvé sur le design et sa sémantique de conversion.

Rédigé par le modèle d'indexation à partir du texte de l'issue.