Is else outside for loop, if yes why else is not executing?

Question

numbers = [10, 20, 33, 55, 39, 55, 75, 37, 21, 23, 41, 13]

for num in numbers:
    if num % 2 == 0:
       print(num)
       break
else:
   print(num)

In the above code i do have else block corresponding to for loop and which is not getting executed. can someone guide me why it is not executing ?

The "else" is executed only if the loop isn't exited by "break" or exception but normally. — Michael Butscher, Oct 24 '19 at 22:08
The question isn't clear. `else` is not outside the `for` loop, it's part of the `for` statement itself. — Barmar, Oct 24 '19 at 22:11
This script prints the first even number. If there are no even numbers, it prints the last odd number. Is that what it's supposed to do? — Barmar, Oct 24 '19 at 22:12
check my answer @Anuvicleo `else` is outside of the loop please read it completely — Ryuzaki L, Oct 24 '19 at 22:17
See https://stackoverflow.com/questions/9979970/why-does-python-use-else-after-for-and-while-loops — Barmar, Oct 24 '19 at 22:20
the else will only execute if you didnt break from the loop, like @Deadpool said in his answer. I have also posted an answer with sample tests that hopefully explains the `for` and `else` construct — Chris Doyle, Oct 24 '19 at 22:22

Ryuzaki L · Accepted Answer · 2019-10-24T22:22:53.790

4

Yes the else block is corresponded to for loop, but it will execute only if break is NEVER executed. Since you have the even numbers in numbers list break is executed and which is why else is not executed

for num in numbers:
  if num % 2 == 0:
     print(num)
     break
else:
  print(num)

Try with this list number=[11,22,33], else block will get executed, for more information 4.4. break and continue Statements, and else Clauses on Loops

Python has different syntax where Loop statements may have an else clause

Loop statements may have an else clause; it is executed when the loop terminates through exhaustion of the iterable (with for) or when the condition becomes false (with while), but not when the loop is terminated by a break statement. This is exemplified by the following loop, which searches for prime numbers:

edited Oct 24 '19 at 22:22

answered Oct 24 '19 at 22:09

Ryuzaki L

37,302
12
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i have edited the question, please can you answer again – Anuvicleo Oct 24 '19 at 22:14
2

@Anuvicleo This answers the question. The `else` block is only executed if there are no even numbers in the list. – Barmar Oct 24 '19 at 22:15
is else outside or inside for loop? – Anuvicleo Oct 24 '19 at 22:17
1

Yes it is outside of the `for` loop please read my answer completely @Anuvicleo – Ryuzaki L Oct 24 '19 at 22:19
why break statement is affecting 'else' from being executed since as you said 'else' is outside for loop – Anuvicleo Oct 24 '19 at 22:22
1

read the documentation that i pointed to, it is a valid syntax in python, you can have `else` block for `Loop statements` @Anuvicleo In your case that else is dedicated to above `for` loop – Ryuzaki L Oct 24 '19 at 22:24

user3503711 · Answer 2 · 2019-10-24T22:08:27.673

0

There is no "if" for that else. I think you need something like this:

numbers = [10, 20, 33, 55, 39, 55, 75, 37, 21, 23, 41, 13]

for num in numbers:
    if num % 2 == 0:
        print(num)
        break
print(num)

edited Oct 24 '19 at 22:08

answered Oct 24 '19 at 22:07

user3503711

1,623
1
21
32

score 0 · Answer 3 · answered Oct 24 '19 at 22:09

0

Indentaion seems to be wrong, try this.

for num in numbers:
    if num % 2 == 0:
        print(num)
        break
    else:
        print(num)

answered Oct 24 '19 at 22:09

User

101
1
9

1

It depends on what it's supposed to do. – Barmar Oct 24 '19 at 22:09
its perfectly valid for a `for` loop to have an `else` clause – Chris Doyle Oct 24 '19 at 22:11
Totally, but he seems to be more concerned about indentation. – User Oct 24 '19 at 22:13
This will print all the odd numbers up to the first even number, and then print that even number. – Barmar Oct 24 '19 at 22:14

score 0 · Answer 4 · answered Oct 24 '19 at 22:21

I think its better to demonstrate this with varying tests. So a for loop can have an else block. the else block is only executed if the loop completed normally. I.E there was not break in the loop. if we create a function that takes a list and a divider. we can see that if the if condition is matched and we print then break, the else block is never run. Only if we run all the way through the loop without break then the else is executed

def is_divisable_by(nums, divider):
    for num in nums:
        if num % divider == 0:
            print(num, "is divsiable by ", divider)
            break
    else:
        print("none of the numbers", nums, "were divisable by", divider)

numbers = [1, 6, 3]
numbers2 = [7, 8, 10]
is_divisable_by(numbers, 2)
is_divisable_by(numbers, 7)
is_divisable_by(numbers2, 4)
is_divisable_by(numbers2, 6)

OUTPUT

6 is divsiable by  2
none of the numbers [1, 6, 3] were divisable by 7
8 is divsiable by  4
none of the numbers [7, 8, 10] were divisable by 6

Is else outside for loop, if yes why else is not executing?

4 Answers4