Nested Loops

Question

Can you please explain this code for me? Thanks.

for i in range(1,10):
is_prime = True
for k in range(2,i):
if (i%k) == 0:
print(i, " is divisable by", k)
is_prime = False
if is_prime:
print(i, " is prime ")

Answer 1

Felix bro it's better to see on YouTube for better understanding while it's hard to understand in comments.... don't worry u will get it ..👍😎

Answer 2

In the second loop is statement that check which number from the first loop( "possibles prime numbers") is divisible by any number from range from 2 to number. If the number is divisible by any number in this range the statement marks the number as non-prime number(is_prime= False). Else it prints the number.

Answer 3

Felix Do u know what is the prime number?
If u know try to think about this code. If u will have trouble with it I can explain.

Answer 4

outer for loop: test for numbers 1-10 if they are prime or not
By default say it is a prime.

inner loop: test if the number is divisible by any number between 2 and itself (excluded)
That is done with the modulus operator % which tells you the rest/remainder of a division.

So e.g. for 5 it goes like this:
5%2 = 1 --> not divisble by 2
5%3 = 2 --> not divisible by 3
5%4 = 1 --> not divisible by 4
So the if-condition is always wrong and is_prime will stay true.

For the number 4 however, you get:
4%2 = 0 --> divisable by 2
You enter the if-branch and is_prime is set to false.
4%3 = 1 --> not divisable by 3

You see, even if you already know that it is not a prime, the loop continous. So for just detecting primes it is quite in-effecient for larger numbers.
Also to show every number for which it is divisable it is not as efficient, since for e.g. 8 you know that if it is divisable by 2, it is also divisable by 4. More sophisticated methods exist, but this a nice start to get familiar with it :)

Answer 5

Yes, I know what prime number is but I'm having trouble to understand the codes. Can you please help me understand? Thanks.

Answer 6

I got this already. I do understand the codes now from range() to indentation. Thanks for your reply.

Answer 7

you know C language??
example :
In C language,
for(initialisation,condition,inc/dec operation)
{
statements;
}

In python language,

for i in range(initialisation starts with given number here , limits upto n number and use every time less than conditions here, how many numbers increment/decrement ):

example :

'''for(i=1;i<n;i++) -> in c language '''
//i++ -> i=i+1...i.e increment by 1

for i in range(1,n,1):