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Python Python Basics (2015) Logic in Python Around and Around

Mariya Shklyar
Mariya Shklyar
1,022 Points
Posted by Mariya Shklyar
Mariya Shklyar
1,022 Points

Loops and if conditions if num % 2 == 0

In th Round and Round video, in about 3:00 Kenneth talking about how to use 'if' in 'for' loop. I can't undestand what the condition is. I thought we use '/' for division. What is '%'? Why and what is == 0? How do use concept of index here? If responding, please consider that Python is the first language I'm learning.

john larson
john larson
16,594 Points

I didn't look at those posts yet but I will. I guess what I meant was: x%2 = 0 result is even. x%2 =1 result is odd. cause 1%2 = 1, at least in python calculations or at least in my python console.

2 Answers

Sky Lu
Sky Lu
1,260 Points
Sky Lu
Sky Lu
1,260 Points

Hi Mariya,

The operator % here is for division, it will return remainder.

In this case:

if num % 2 == 0

means number divide 2 , and the remainder is 0, then it will print out.

in the video, num got [1, 2, 3, 4]

1 ÷ 2 the remainder is 1

2 ÷ 2 the remainder is 0

3 ÷ 2 the remainder is 1

4 ÷ 2 the remainder is 0

That's why it print out is 2 and 4

if you make the num to [1, 2, 3, 4, 5, 6]

the result will be 2, 4, 6

ivettelindsay
ivettelindsay
4,008 Points

Thank you :-)

Michael Rathbun
Michael Rathbun
1,624 Points
Michael Rathbun
Michael Rathbun
1,624 Points

Yes ok this is what I was looking for as well. thank you for asking Mariya ! Kenneth is a great teacher, but sometimes he buzzes through things like this and I have to turn the speed down and stop the video to ingest it properly.

tobiaskrause
tobiaskrause
9,160 Points
tobiaskrause
tobiaskrause
9,160 Points 
for num in [1, 2, 3, 4]:
    if num % 2 == 0:
        print(num)

he just checked which of these numbers are even. Because the if statement will trigger for each element in the array. So for the number 2 it would print 2...because the statement is true...and for the number 3 it would print nothing cause the statement is false.

john larson
john larson
16,594 Points

Tobias, I get the basic concept that % is used to check if a number is even. But when I run your numbers I get different results. I get 10%4 = 2. I havn't seen the % used like this yet, but I've heard mention of it. I'm hoping to understand

tobiaskrause
tobiaskrause
9,160 Points

Sry Sry. I am at work...my brain is not focused at TH :) So modulo is just the reminder of a devision. f. e. 20 % 6 = 2 because you can just get 18 and not 24...and 20-18 = 2

john larson
john larson
16,594 Points

Ok, I see how it works now. returns 0 = even. returns 1 = odd. Did I get that right?

tobiaskrause
tobiaskrause
9,160 Points

Maybe this blog post might help you https://betterexplained.com/articles/fun-with-modular-arithmetic/ Modulo is used in different ways... For example you can say "Hey do something untel x % y == z"

Also