For PySoy, she may be our long-sought salvation from Pyrex.
First to note, PySoy is based heavily on GLib. While much of GLib is redundant to types and functions available with Python's c-api, the GLib functions don't require Python's GIL to be used. This is what allows PySoy to take full advantage of multiple cores and run Python code in parallel with rendering and physics processing.
Second of note, as I wrote in my last post, Pyrex/Cython are not appropriate for PySoy as an overwhelming majority of our code is inside
with nogil:. Many Pyrex/Cython language features, what makes them easy to work with, are thus unavailable to us. The language becomes a burden and "GIL minefield" that makes working with it difficult.
Like Pyrex, Vala "compiles" clean object-oriented code to C, unlike Pyrex we have full and direct access to all datatypes and classes without the GIL. Like Pyrex, Vala needs pseudo-headers to instruct it how to use C libraries, unlike Pyrex the .vapi files give us an OO API for working with those libraries.
This was the real deal maker though; Vala is flexible enough to use PyObject and family directly. Not only do we get GObject access but with python.vapi, full OO access to Python's c-api with automatic incref/decref and easy Python/C type conversion.