python prime number algorithm

[zowhair]

I have a problem
https://docs.python.org/3/tutorial/controlflow.html

>>>for n in range(2, 10):
     for x in range(2, n):
         if n % x == 0:
             print(n, 'equals', x, '*', n//x)
             break
     else:
         # loop fell through without finding a factor
         print(n, 'is a prime number')

All goes good but when n reaches 9 then how x will be equal to 9, as in all previous steps x will not proceeds from 2. As in simple 9 % 2 == 0 will be false and else part should be execute but here this is calculating 9 % 3 == 0 : and printing the statement. I am stucked here, kindly guide me.

[squenson]

I don't see anything wrong with your code, except that it could be more efficient. 9 is not a prime number as it is equal to 3 * 3. The output I get is:

2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3

As indicated below the example in the link, the else belongs to the for loop, NOT to the if statement.

[buran]

Probably this would help to understand the execution

for n in range(2, 10):
    for x in range(2, n):
        print ('n={}, x={}, n%x={}'.format(n, x, n%x))
        if n % x == 0:
            print('{} equals {} * {}'.format(n, x, n//x))
            break
    else:
        # loop fell through without finding a factor
        print('{} is a prime number'.format(n))

[zowhair]

Got it... Thanks alot guys