Interfacing Fortran, C, C++, and Python: Memory allocation for arrays that pass the API

Memory allocation for arrays that pass the API

Library side

Advantage:

• Caller does not need to know the array sizes a priori.

Disadvantage:

• Risk of a memory leak (garbage collection on the Python side).

Client side (recommended)

Advantages:

• Let the caller decide how memory is allocated.
• Reduced risk of a memory leak.

Disadvantage:

• You need to know array sizes.
• Requires extra layer on the Python side.

Example

Consider these two functions:

double *get_array_leaky(const int len)
{
    double *array = new double[len];

    for (int i = 0; i < len; i++)
    {
        array[i] = (double)i;
    }

    return array;
}

void get_array_safe(const int len, double array[])
{
    for (int i = 0; i < len; i++)
    {
        array[i] = (double)i;
    }
}

How can we use the second one?

from cffi import FFI

def get_array_safe(length):
    ffi = FFI()
    lib = ffi.dlopen(...)

    array = ffi.new("double[]", length)
    lib.get_array_safe(length, array)

    return array

• Demonstration: Client-side or library-side memory allocation with Python CFFI.
• You need to hold on to the object for as long as you need the memory on the library-side.

Questions

• How can you make the API function return a Python list or dict?
• Can you implement generators?