what is the difference between these two programmes

Question

b=input("Enter number : ")
for n in range(2, b+1):
     for x in range(2, n):
         if n % x == 0:
              break
     else:
          print n

This program prints prime numbers up to n Out put is

Enter number : 10
2
3
5
7

and

b=input("Enter number : ")
for n in range(2, b+1):
     for x in range(2, n):
         if n % x == 0:
              break
         else:
              print n

out put is

Enter number : 10
3
5
5
5
7
7
7
7
7
9

@MMF - I know it's weird, but that indentation difference actually changes how this code works. http://stackoverflow.com/questions/9979970/why-does-python-use-else-after-for-and-while-loops — thegrinner, Oct 21 '16 at 15:17
Before the editted, the second program had a `for else` statement, and now I'm not sure since it's the same.... But if it was true to have a for else, then the one with for else will print `n` once the for loop ends. Edited: Guys please stop editing it, is it a `for else` or not... — MooingRawr, Oct 21 '16 at 15:17
@kloe the indentation in your first block is important. Are the `for` and `else` at the same level of indentation? — thegrinner, Oct 21 '16 at 15:21

MooingRawr · Accepted Answer · 2016-10-21T15:28:36.323

b=input("Enter number : ")
for n in range(2, b+1):
     for x in range(2, n):
         if n % x == 0:
              break
     else:
          print n

prints out n if n % x has no remainder and only the first correct value since it breaks out.

b=input("Enter number : ")
for n in range(2, b+1):
     for x in range(2, n):
         if n % x == 0:
              break
         else:
              print n

prints out every n that has a non zero remainder until the first zero remainder appears.

More on how for else works:

for else will run the for loop and then run the else right after the for loop finishes. In your case the for loop ends at a certain point and then prints the resulting value where it ended at.

for x in range(10):
    print x
else:
    print "hello world"

Take this for example. It prints out :

0
1
2
3
4
5
6
7
8
9
hello world

Why is this useful? Well your program gives a very nice example on why it is. We want to exit the for loop for a certain condition that passed, and then do something after we've found that condition (if we've found the passing condition else we just run it anyways). So if condition is met in for loop run this, or run this at the end of the for loop always.

Back to your question, basically the first one finds the factors of the number given, and the second one finds the non factors of the number given.

sorry i meant ow does the else statement work on the first problem — kloe, Oct 21 '16 at 16:56
Read my answer, I covered it. The `else` statement runs after the for loop ends, either by out of items to iterate, or by a break — MooingRawr, Oct 21 '16 at 17:16

score -1 · Answer 2 · answered Oct 21 '16 at 15:19

They are identical

XXXX:tmp anthony$ cat > one.txt
b=input("Enter number : ")
for n in range(2, b+1):
     for x in range(2, n):
         if n % x == 0:
              break
         else:
              print n
XXXX:tmp anthony$ cat > two.txt
b=input("Enter number : ")
for n in range(2, b+1):
     for x in range(2, n):
         if n % x == 0:
              break
         else:
              print n
XXXX:tmp anthony$ diff one.txt two.txt
XXXX:tmp anthony$

Wrong, one of them has a `for else` statement, but people kept editing it to change it — MooingRawr, Oct 21 '16 at 15:20

what is the difference between these two programmes

2 Answers2