I'm a little confused about python logic ; and my question to the modulus in determining odd and even

Question

I want to ask, the code below produces triangles * which are only odd.... but I'm confused... can anyone explain why the modulus can produce odd triangles and also why the else command is needed? (note I don't really understand modulus)

count = 1
while True :
    if count % 2 :
        print ('*'*count)
        count += 1

    else:
         count +=1
         continue
    
    if count > 10 :
        break

Answer 1

The expression if (count % 2): means if the count is odd.

Explanation:

count % 2

• will always equal 0 if count is an even number

• will always equal 1 if count is an odd number

• if count % 2 when count is odd breaks down to if 1 which is always True

• if count % 2 when count is even breaks down to if 0 which is always False

For your second question the else actually isn't necessary, it could be rewritten like this

count = 1
while True:
    if count % 2 :
        print ('*'*count)
    count += 1
    if count > 10 :
        break

When you consider a standard equalateral triangle made of * :

this is what it looks like using only odd numbers..

       *
      ***
     *****
    *******
   *********
  ***********
 *************

this is what it would look like using evens and odds

      *
     **
    ***
   ****
  *****
 ******
*******

Answer 2

Modulus in this case differentiates between odd and even numbers. In your case, as you can see in the printed pyramid, you only have odd values - 1,3,5 etc. You are in the "if" part when you have an even number, and in the else part for the off.

I suggest you put more print statements in the program to see it's behavior in greater detail.

Answer 3

The if check for return value = 1, not zero. If you try to put if(count % 2 == 0) for example, you will notice non odd print.

Answer 4

Your logic could potentially be simplified:

for i in range(1, 12, 2):
    print('*' * i)

Explanation:

The range operator accepts a stop value (non-inclusive) and a step value, which defaults to 1. Here we pass step=2 , so we only iterate over the odd numbers in the range.

Out:

*
***
*****
*******
*********
***********

Answer 5

Modulo, or modular division is like grade school integer division where you don't compute a decimal part, but rather just a whole part, and a remainder. Specifically modulo throws out the whole part, and only keeps the remainder. The opposite of that is integer division, which throws out the remainder: 9//2 == 4 #quotient 9%2 == 1 #remainder

• while True: Do this forever (or until break or an uncaught error)
  • if (count % 2): Do this if count is Odd: (count % 2) will be 1 if odd, and 0 if even. 1 will cast to True, and 0 will cast to False for the if condition.
    • print('*'*count) construct a string by repeating the string "*" by count times, and print it.
    • count += 1 increment the count variable
  • else do this if count is even (corollary to prior statement)
    • count += 1 increment the count variable
  • if count > 10: when count variable is greater than 10
    • break exit the while True loop