BOM Low Level Code Calculator Script (Python Generator)

import csv
import sys
from collections import defaultdict

sys.setrecursionlimit(10000)

edges = defaultdict(list)
with open("bom_edges.csv", newline="", encoding="utf-8-sig") as f:
    for row in csv.DictReader(f):
        parent = row["parent_item"].strip()
        child = row["component_item"].strip()
        if parent and child:
            edges[parent].append(child)

items = set(edges.keys())
for kids in edges.values():
    items.update(kids)

level = {}


def walk(node, depth, path):
    if node in path:
        raise ValueError("BOM loop: " + " > ".join(path + [node]))
    if depth <= level.get(node, -1):
        return
    level[node] = depth
    for child in edges.get(node, []):
        walk(child, depth + 1, path + [node])


children = set()
for kids in edges.values():
    children.update(kids)

roots = sorted(items - children)
for root in roots:
    walk(root, 0, [])

if len(level) < len(items):
    print("Warning: items only in a loop have no level:", sorted(items - set(level)))

with open("low_level_codes.csv", "w", newline="", encoding="utf-8") as out:
    w = csv.writer(out)
    w.writerow(["item", "low_level_code"])
    for item in sorted(level, key=lambda i: (level[i], i)):
        w.writerow([item, level[item]])

print("Items:", len(items), "End items:", len(roots), "Max level:", max(level.values()))