On-topic: alternate Python implementations

[Stefan Behnel]

Steven D'Aprano, 04.08.2012 09:49:
> On Sat, 04 Aug 2012 08:40:16 +0200, Stefan Behnel wrote:
>> And not to forget Cython, which is the only static Python compiler that
>> is widely used. Compiles and optimises Python to C code that uses the
>> CPython runtime and allows for easy manual optimisations to get C-like
>> performance out of it.
>>
>> http://cython.org/
> 
> Cython is great, but I question that it is a *Python* implementation. 
> That's not a criticism of Cython, but it is different from Python. Take 
> this example code from the tutorial:
> 
> from libc.math cimport sin
> 
> cdef double f(double x):
>     return sin(x*x)
> 
> If that's Python code, then I'm Ethel the Aardvark.

We never met in person, so I can't comment on the last part.

However, the above is Cython code and, yes, that's a different language.
Note that it uses a different file extension: ".pyx". Try putting the above
code into a .py file and compiling that. Cython will reject it and tell you
that "cimport" is not valid Python syntax.


> Cython is very Python-like, but there is no doubt in my mind that it is a 
> superset of Python and therefore a different language.

As long as you don't use any features of the Cython language, it's plain
Python. That makes it a Python compiler in my eyes. The fact that you can
easily use C features to optimise your code (also in Python syntax, BTW)
doesn't impact that.

You mentioned a couple of other implementations and I'm sure they have
features (and bugs) that CPython doesn't have. Interaction with Lisp code
in CLPython, for example. I don't think additional features or language
implementation bugs make a Python implementation non-Python per se.

Also note that most of the less widely known "alternative Python
implementations" do not even publish their results of running the CPython
test suite, so how do you actually know they can run Python code?

Stefan