"""Synthetic local application example. No network or database calls."""
import json
courses={"C1","C2"}
enrollments=[("E1","C1"),("E2","C2"),("E3","C9"),("E4",None)]
result={"ready":[],"held":[]}
for id,parent in enrollments:
    if parent is None or parent in courses: result["ready"].append(id)
    else: result["held"].append({"id":id,"reason":"missing_parent","parent":parent})
assert result["ready"] == ["E1","E2","E4"]
assert result["held"] == [{"id":"E3","reason":"missing_parent","parent":"C9"}]

print(json.dumps(result, indent=2, ensure_ascii=False))