answer

import cffi
ffi = cffi.FFI()
ffi.cdef("""
        extern struct intensity_data {
            double nw;
            double ne;
            double sw;
            double se;
            int error;
        } _intensity_data;

        struct intensity_data jpeg_intensities(const char *file_name);
        struct intensity_data png_intensities(const char *file_name);
""")
ffi.set_source('mymod', '''
        extern struct intensity_data {
            double nw;
            double ne;
            double sw;
            double se;
            int error;
        } _intensity_data;
    struct intensity_data jpeg_intensities(const char * file_name) {
        struct intensity_data a;
        return a;
    };
    struct intensity_data png_intensities(const char * file_name) {
        struct intensity_data a;
        return a;
    };
 ''')
ffi.emit_c_code('/tmp/stam.c')