For loop that handles if a list could be None instead of having items in a list.

for_loop_or_none.py

# For loop that handles if an item is None instead of having
# items in a list.

# this is a sqlalchemy query, it will either return a list of people with 
# the first_name of 'Justin' or if there is no person with that first name
# it will return None. This is just an example of when a variable might be 
# a list with list items or None.
# people = Person.query.filter_by(first_name='Justin'.all()

# I'm specifically setting people to None here because I'm not calling the sqlalchemy query above.
# If people was a list that contained items, the print statements in the for loop would be called.
# Since people is set to None, nothing will be printed because empty list in the 'or []' section 
# is what is evaluated.
people = None
for person in people or []:
    print(person.first_name)
    print(person.last_name)



# unlrelated comprehension equiv but same concept
result = [do_something(item) for item in a_list() or []]