Cython header directive and __future__

Question

What is the correct way to utilize Cython header directives AND utilize a future import? Python 2.7.x

Example:

1: from __future__ import division
2: #cython: boundscheck=False
3: #cython: wraparound=False
<strike>4: #cython: cdivision=True</strike>
4: #cython: cdivision=False

This ensures that division works as expected (using the future version), but I am unsure whether the directives are being observed. Swapping line 1 with line 4 causes division to revert to the standard Python 2.x method.

Answer 1

As commented by @user2357112 #cython: cdivision=True contradicts from __future__ import division. This code is illustrative:

#cython: wraparound=False
#cython: boundscheck=False
#cython: nonecheck=False
#cython: profile=False
from __future__ import division

def main():
    cdef double i, j
    i = 0
    j = 2
    print 1/j
    print 1/i
    print 1/2

raising:

    print 1/i
ZeroDivisionError: float division

Adding #cython: cdivision=True it will give:

0.5
inf
0

where you can see the 1/2 being processed as a floor division.

In this case I would recommend to apply the float point 1/2. wherever you want a float division when using Python 2.x...

Swapping the lines as you mentioned:

from __future__ import division
#cython: wraparound=False
#cython: boundscheck=False
#cython: nonecheck=False
#cython: profile=False
#cython: cdivision=True

will cancel all the Cython global directives, because they "must appear before any code (but can appear after other comments or whitespace)".