Use multi-phase initialisation (PEP 489)

[AA-Turner]

Multi-phase initialisation was introduced in PEP 489 for Python 3.5. It replaces the previous 'single-phase' mechanism by splitting the module creation process into creation and execution phases. Quoting from the documentation:

Extension modules created this way behave more like Python modules: the initialization is split between the creation phase, when the module object is created, and the execution phase, when it is populated. The distinction is similar to the __new__() and __init__() methods of classes.

This means that Python can determine the capabilities a module supports before executing it. It is a more flexible approach, and has been recommended for several years. This is of particular interest to me as MarkupSafe is one of the few extension modules in Sphinx's dependency tree, and currently prevents using subinterpreters with Sphinx.

You may have already seen that there is a proposal to deprecate single-phase init
, though this would currently be documentation-only.

A

[AA-Turner]

See #495 for a proposed implementation.

A

[davidism]

I'll merge this for 3.0.3, but I do plan to use Rust #438 and release 4.0 at some point, so PyO3 support would be great.

I also saw @zackw talk about interruptible extension moudles at PyCon US https://www.youtube.com/watch?v=_XnYI2Kcck0, and would like to support that if possible. Does that need support in PyO3 as well?

[zackw]

@davidism Right now, I think you have to manually check for signals when using PyO3. I haven't actually used PyO3 at all myself, and the thing with cancel handles near the end of my talk was a hypothetical future feature. I'd be happy to discuss this further with you, the PyO3 maintainers, and anyone else interested, but this bug obviously isn't the right venue :) (not sure what the right venue is, though)