How to use a C function with complex types in Python?

Question

I decided to port some of my Python functions to C, mostly following this simple tutorial. Problem is that my C function returns a complex float, and there\'s no correspondi

Answer 1

Create a small C wrapper function:

void integrand_wrapper(float *re, float *im, double r, double z)
{
    float _Complex  result;
    float _Complex  theta = (*re) + I*(*im);
    result = integrand(theta, r, z);
    (*re) = creal(result);
    (*im) = cimag(result);
}

The re and im pointers hold the real and imaginary parts of theta when called, and the real and imaginary parts of the result afterwards.

In your Python code, call integrand_wrapper() using e.g.

def integrand(theta, r, z):
    global _integr
    theta = complex(theta)
    re = c_float(theta.real)
    im = c_float(theta.imag)
    _integr.integrand_wrapper(byref(re), byref(im), c_double(r), c_double(z))
    return complex(float(re), float(im))

Note that if integrand() is defined in a binary library you cannot modify, you can always create another dynamic library containing only integrand_wrapper, that is dynamically linked (in C) to the original binary library.

Overall, I don't think the added overhead is significant at all. It is certainly worth testing.