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

Initialize your student.subjects and subject.books with [], and then it'll work. Just as what @user714965 said.

or, use list-comprehension:

for s in [stu if stu.has_key(subjects) for stu in students]:
    for subject in [subj if subj.has_key(books) for subj in s.subjects]:
         lists= [(s.name, s.class, subject.name, book.name) for book in subject.books]
              print r'\n'.join(r','join(lists))

or

if your loop is not very deep,try something like this:

fn= s.has_key('subjects') and (lambda s: /do sth. with s/ ) or (lambda s: /do sth. else with s/)

in your loop, use the fn like this,

[fn(s) for s in students ]