If-else indentation

Question

I am playing with python3.5 right now. I was working on a simple code, to find the prime numbers less than a given integer. I solved the code more by mistake and I don't know why. This is the code:

n=int(input('Enter a numeric value: '))

for num in range(2, n+1):
    if num>1:
        for i in range(2, num):
            if (num%i)==0:
                break
        else:   
            print(num)

What I don't seem to understand is why if i write the code like above it gives a correct answer, and if i write the else statement with one more indentation, the output is different. Ex:

Enter a numeric value: 10

3

5

7

9

for:

...if num>1:
    for i in range(2, num):
        if (num%i)==0:
            break
        else:   
            print(num)

I feel the need to mention that I just started to learn python so please take me slow:D

You don't need to write `if num>1:` since `num` will iterate in the range 2..(n+1) which means that `num` will _always` be greater than 1. — Thomas Baruchel, Nov 14 '15 at 14:40
I mostly let it there so I can fastly modify the code if I want a prime no. in a certain range. Ex. I enter `low=input()` for the bottom value of the range. — Claudiu B, Nov 14 '15 at 14:44

score 0 · Accepted Answer · answered Nov 14 '15 at 14:21

0

The else is associated with the for. Indenting it farther associates it with the if.

An else after an if runs if the if didn’t
An else after a for runs if the for didn’t break

You want the latter behaviour, since you break if you found a factor for the number.

answered Nov 14 '15 at 14:21

Ry-

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Thank you. Sometimes I really get mind-blocked by such simple things... – Claudiu B Nov 14 '15 at 14:28

If-else indentation

1 Answers1