这些for循环中哪个更有效/更好的循环编码方式

Question

Which is better between these two for-loops in python? I have "assumed" the compiler would be smart enough to do the json.loads just one time and, on its own, store the data in a temporary variable so that it could maintain the iterator needed to process the for-loop. But then I started to wonder if I was mistaken and that the first style would be causing unwarranted extra steps.

for employee in json.loads(response.content)

OR

temp = json.loads(response.content)
   for employee in temp

Answer 1

Although both are essentially the same, there's one good reason to favor a temporary value: it lets you catch any errors in the call to json.loads before trying to iterate over the result. This is consistent with keeping the code in a try statement as focused as possible.

try:
    employees = json.loads(response.content)
except JSONDecodeError:
    # Maybe log an error message
    # Maybe just reraise the exception
    employees = []

for employee in employees:
    ...

Answer 2

It's fairly clear from the documentation :

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

The expression list is evaluated once;

So your worry is unfounded, and the first way is preferable unless you want to reuse the data again or writing it on the for line would make the line too long.