How can I make the efficent for loop in Python?

Question

I am writing the csv file in python and there are four levels of nested objects. like

I need to show the csv like this

StudentName, StudentCla

Answer 1

Assuming s.subjects is None or some other False value when there are no subjects, and likewise for books

for s in students:
    for subject in s.subjects or []:
        for book in subject.books or []:
            writer.writerow(s.name, s.class, subject.name, book.name)

More generally, you can write

for s in students:
    for subject in s.subjects if  else []:
        for book in subject.books if  else []:
            writer.writerow(s.name, s.class, subject.name, book.name) 

Where is whatever expression makes sense