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Python Python Basics (2015) Letter Game App Even or Odd Loop

Enzo Cnop
Enzo Cnop
5,157 Points
Posted by Enzo Cnop
Enzo Cnop
5,157 Points

How does this code check if the number is even/odd?

I passed the challenge my copy and pasting from another help thread. I don't understand how this concept works. How does the 'even_odd' function check against the randint? I see the 'if even_odd(randint):' line, but how does this decide if it is true or not against 5? Also, the 'start -= 1' line seems to be part of the 'else' statement. How does it run if the first function goes through? 

import random

start = 5

def even_odd(num):
    return not num % 2

while start:
  randint = random.randint(1, 99)
  if even_odd(randint):
    print("{} is even".format(randint))
  else:
    print("{} is odd".format(randint))
  start -= 1

Why can't the code read

import random

start = 5

def even_odd(num):
    return not num % 2

while start is True:
    num = random.randint(1, 99)
    even_odd(num)
    print("{} is even".format(num))
else:
    print("{} is odd".format(num))
start -= 1

I'm guessing this doesn't work because start is never modified, and as a result it will always = 5, meaning it will always be True?

1 Answer

Steven Parker
Steven Parker
231,261 Points
Steven Parker
Steven Parker
231,261 Points

The modulus operator is used to determine even/odd status.

That's what "num % 2" is doing. The modulus, or remainder, will be 1 for odd numbers and 0 for even numbers. Then the "not" operator is used to flip that to make the result True for even numbers and False for odd.

And "start -= 1" is not part of the else statement because it is not indented far enough. Anything part of the else would have to be indented more than the else itself.

Enzo Cnop
Enzo Cnop
5,157 Points
Enzo Cnop
Enzo Cnop
5,157 Points

Thank you for your reply. I understand now what is happening with the 'not num % 2' -- I still would like to know why start = 5. Could start = True in this situation and produce the same result?

Steven Parker
Steven Parker
231,261 Points
Steven Parker
Steven Parker
231,261 Points

Since start is being used as a counter, it needs to be number. Each time through the loop, the value is reduced by one. When it reaches 0, the loop stops running.

Enzo Cnop
Enzo Cnop
5,157 Points
Enzo Cnop
Enzo Cnop
5,157 Points

Aha! Now I understand what is happening. The code takes a random number and checks if it is even or odd 5 times before breaking. If the challenge had asked us to do this in the first place, I think I would have been less confused. Thank you again!