python - How many times does a for loop evaluate its expression list?

Question

I have the following code:

list1 = [4,1,2,6]
for elem in sorted(list1):
    #some task

I was wondering how many times does Python sort the list using the sorted() method? Is it for each iteration or just once?

In other words is the following code more efficient?

list1 = [4,1,2,6]
list1 = sorted(list1)
for elem in list1:
    #some task 

Answer 1

In both code examples, the list is sorted only once.

The expression on the right of the in operator in a for-loop header is evaluated just once, before looping commences. You can read about this in the documentation:

for_stmt ::=  "for" target_list "in" expression_list ":" suite
              ["else" ":" suite]

The expression list is evaluated once; it should yield an iterable object.

In fact, the second code example is less efficient because there is an unnecessary assignment.