Looking on simple example of cython code I wonder if CPython interpreter needed some hard-coded hacks to understand cython syntax (e.g. cdef int N) or if it is implemented using some concepts of standard python syntax (e.g. functions, classes, operators etc.)
I mean, I can roughly imagine how the cython backend can be implemented (c-code generation, compilation etc.), but I don't understand how the frontend syntax can be integrated within standard python interpreter without touching the python interpteter itself (i.e. without extending python language beyond standard).
What is cdef ?
In other words, what cdef actually is? Is it a function, operator, or some new keyword? I would understand N = cedef(int) - that would create instance of some class derived from int. But written like that, I don't see how these 3 tokens even interact (1 cdef, 2 int, 3 N) ?
Does the for-loop actually iterate?
if you write code like this:
cdef int i,N = 1000000
cdef double f = 0
for i in xrange(N):
f += (i*i)
print f
The loop for i in xrange(N): is normal python loop. What prevents python interpreter to uselessly iterate 1000000 iterations before cython compile it into to C-code?
Does it work something like this:
N is an instance of some class cdef. xrange call N.__int__() which returns 1, passing the loop only once. The expression f += (i*i) contains only cdef objects, so cython can redefine __add_(), __set__(), __get__() functions in a way that generate C-code for f+=(i*i)
But then I still don't see how the construct for i in xrange() is send to cython, to generate C code from it.
Anyway, it seems quite complicated and fragiel, so perhaps it must be otherwise