Szathmáry László honlapja @ DEIK | DLang / Passing a list of integers

We want to pass a list of integers from Python to D.

Notes:

In Python, a list (e.g. li = [1, 2, 3]) is different from a C array. If we want to pass it to a D function, first we need to convert it to a C array.
A D slice is a fat pointer, a combination of a pointer and length. So we pass these two data to the D function.

Makefile:

cat:
	cat Makefile

so:
	# -shared → build a shared library
	# -fPIC → position-independent code (needed on Linux for shared libs)
	dmd -shared -fPIC mylib.d -of=libmylib.so

run:
	./main.py

D code

(1) D code

extern (C) int mysum(const int* numbers, const size_t length)
{
import std.algorithm : sum;

// convert pointer + length into a D slice
auto slice = numbers[0 .. length];
return slice.sum();
}

Python code

(2) Python code

#!/usr/bin/env python3

from cffi import FFI

ffi = FFI()
lib = ffi.dlopen("./libmylib.so")
ffi.cdef("int mysum(const int* numbers, const size_t length);")

def carray(lst):
"""Convert a Python list of ints to a cffi C array"""
return ffi.new("int[]", lst)

def main():
li = [1, 2, 3]
print(lib.mysum(carray(li), len(li)))

if __name__ == "__main__":
main()

After this, you can execute your Python program:

$ ./main.py
6