OpenSCAD parts system...

export.py

import subprocess
import sys

f = sys.argv[1]
openscad = 'openscad-nightly'

result = subprocess.check_output([openscad, '--export-format', 'echo', '-o', '-', f])

exported = set()

for line in result.decode().split('\n'):
    if line.startswith("ECHO: ") and "PART:" in line:
        part = line[13:-1]
        if part not in exported:
            subprocess.check_call([openscad, '-D', f'$part="{part}"', '-o', f'{part}.stl', f])
            exported.add(part)

main.scad

use <part.scad>

# Wrap each separate part in the "part" module like this:

part("a") cube(10);
part("b") sphere(5);

# Running the export.py on this file will export a.stl and b.stl
# If you define $part at the top of this file, only that part will be previewed.
# If $part is undefined or doesn't match anything, everything will be previewed.

part.scad

# The part module eachoes the name of the part so that the exporter
# script can parse a list of all parts. Then it applies ! to children
# iff $part = this part.

module part(name) {
    echo(str("PART: ", name));
    if($part == name) {
        !children();
    } else {
        children(); 
    }
}