alt Hacker NewsPyPy handled this by implementing PyPy in a restricted minimal subset of Python that they called RPython, and that seemed to work out well for them.
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paulddraper • yesterday at 4:54 PM
The key difference is that RPython is actually a compiled language.
I.e. PyPy DOESN'T have an interpreter written in an interpreted language.
I was never a user of PyPy but I really appreciated the (successful) effort to cleanly extract from Python a layer that of essential primitives upon which the rest of the language's features and sugar could be implemented.
It's more than just what is syntax or a language feature, for example RPython provides nts classes, but only very limited multiple inheritance; all the MRO stuff is implemented using RPython for PyPy itself.