CODEWITHSUNDEEP
pythonccythondoctest
0p3r4t0r
0p3r4t0r

Reputation: 693

How do I run a doctest from Cython?

The Setup

  1. Let's say I have a script fib.py. With some doctests in it.

    def fib(n):
    """Return the nth number in the Fibonacci sequence.

    >>> fib(0)
    0.0
    >>> fib(1)
    1.0
    >>> fib(4)
    3.0
    >>> fib(7)
    13.0
    """
    a, b = 0.0, 1.0
    for i in range(n):
        a, b = a + b, a
    return a

if __name__ == "__main__":
    import doctest
    doctest.testmod()

    Everything works as expected and I can confirm that the tests are running by checking the output of python3 fib.py -v.

  2. Alright, now I'm going to translate this into Cython, and for good measure I'll even remove the if __name__ == '__main__' conditional. Let's call our Cython file fib.pyx

    #cython: language_level=3

def fib(int n):
    """Return the nth number in the Fibonacci sequence.

    >>> fib(0)
    0.0
    >>> fib(1)
    1.0
    >>> fib(4)
    3.0
    >>> fib(7)
    13.0
    """
    cdef int i
    cdef double a=0.0, b=1.0
    for i in range(n):
        a, b = a + b, a
    return a

import doctest
doctest.testmod()

  3. Of course we need to compile our Cython. For me that's

    cython --embed fib.pyx
gcc $(python-config --cflags) $(python-config --ldflags) fib.c

    This produces a.out.

  4. If I try ./a.out -v I get . . .

    1 items had no tests:
    __main__
0 tests in 1 items.
0 passed and 0 failed.
Test passed.

What happened to my tests?

(Potentially) helpful links.

Upvotes: 1

Views: 244

Answers (1)

0p3r4t0r
0p3r4t0r

Reputation: 693

Alright, there were a few problems here . . .

First I wasn't really compiling properly. The final result should be a .so file on MacOs/Linux systems and a .pyd file on linux.

Building a Cython module

You can quickly compile by writing a setup.py file

from distutils.core import setup
from Cython.Build import cythonize

setup(ext_modules=cythonize('fib.pyx'))

Depending on your OS and python version running 

python setup.py build_ext --inplace

will produce something like fib.cpython-37m-x86_64-linux-gnu.so

For more info see the relevant Cython docs.

Install pytest modules

pip install pytest
pip install pytest-cython

Running the tests

From the directory where your compiled Cython lives run . . .

pytest --doctest-cython -v

The -v is of course verbose and provides additional output.

From pytest --help | grep cython we can see what this command is doing.

cython:
  --doctest-cython      run doctests in all .so and .pyd modules
  --cython-ignore-import-errors

Upvotes: 1

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