Python -- loop-else basic principle

Question

The following code is from my homework. I have the question and I also have the answer, but I don't understand how to get the answer.

#Question
result = 0
for n in range(3):
 print(n, end=' ')
 result -= 3
else:
 print('| {}'.format(result))
print('done')

#Answer
0 1 2 | -9
done

The for loop is using a range of 0-2, so I expect it to run through the loop all 3 times and produce the '0 1 2' part, but why does it add the 'else' portion? Shouldn't it only use the 'else' portion if the loop statement evaluates as 'False' but how is it false if the loop knows to only run 3 times and none of the first 3 statements evaluate as false? Or does the else always evaluate when it's a loop-else? I assume I'm missing some fundamental knowledge here. TIA

• Ashkan Goleh Pour: its simple like if else , while your loop with statements body ends then your else comes out . its evaluate as break point
• A l w a y s S u n n y: The else keyword in a for loop specifies a block of code to be executed when the loop is finished:
• Kraigolas: "Shouldn't it only use the 'else' portion if the loop statement evaluates as 'False'". The "loop statement" is an iterable, which can be falsy (if it is empty) but it isn't ever False.
• Kraigolas: Does this answer your question? Why does python use 'else' after for and while loops?
• Matt P: @Kraigolas it doesn't answer it directly as most of the examples were for loops that could be evaluated as false (ie if it didn't find the object/flag) but the general conversation is the same and I did learn some helpful info. Thank you for finding that!

Answer 1

We use else with for loops to check that if the for loop has reached the end without a break for exmaple:

for i in range(5):
 print(i)
 if (i == 3):
 break
else:
 print("iterated over the whole range")

this will only print numbers from 0 to 3 and then stop without printing the message because we have broke out of the loop.

note that not many programming languages support putting else after a loop.

Answer 2

A for loop's else clause is executed when all iterations finish executing without interruption (i.e.: without encountering a break).

If a break is encountered within the for loop, the else won't be executed.

See the Python documentation: https://docs.python.org/3/tutorial/controlflow.html#break-and-continue-statements-and-else-clauses-on-loops