Can anyone explain to me what does the "if not x%2:" mean?

Question

I am trying to understand this code but the "if not x%2:" is quite confusing. It has the same result as "if x==2".

count_even = 0
for x in range(1,9):
    if not x % 2:
         count_even+=1

Can you explain to me the "if not x%2:" verbally? I know it is same as some other functions but I want to know how does it work — Yap Zheng Xiang, May 13 '19 at 16:17
If you search on the phrase "Python % operator", you’ll find resources that can explain it much better than we can in an answer here. AMong other things, you'll see that it does *not* have the same result as `if x==2`. — Prune, May 13 '19 at 16:35

score 1 · Answer 1 · answered May 13 '19 at 16:14

1

No, it's not the same, the first statement is a evaluating if x is odd. Why? In python 0 evaluates to False and the % operator is module, that returns the quotient of the two items.

In the second approach you are just saying if x is equal to 2

answered May 13 '19 at 16:14

dnarvaez27

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score 1 · Answer 2 · answered May 13 '19 at 16:15

1

x%2 will return 0 when x is even and 1 when x is odd.

So this if statement evaluates to true when x is even and false when x is odd.

answered May 13 '19 at 16:15

tdammon

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score 1 · Answer 3 · answered May 13 '19 at 17:09

if not x%2

Modulo operator calculates the remainder of number x w.r.t number y. And in your example x is ranging from 1-9 and y is given as 2.

So first, x%2 will evaluate to either 1 or 0 based whether x is odd number or even number respectively.

for example:

for x=1 , x%2 = 1%2 (calculating the remainder) = 1

for x=2 , x%2 = 2%2 = 0

Similarly, x=3, 3%2 = 1 (remainder)

And so on...

Now, if it is even number meaning evaluating to 0 which is equivalent to False and then not operator is negating the result i.e. not(False) == True,hence condition becoming True

So, when if condition is coming out to be True then, your code is incrementing the count of even number.

Hope this helps!.

score -1 · Answer 4 · edited Aug 01 '21 at 18:03

#Hai let me give you one example you can get clarify your doubt !!!

event_squares=[]

for x in range(10):
    if  x%2:  # here conditions True means x is odd(1%2=1(True),3%2=1(True)
        event_squares.append(x*x)

print(event_squares)

output=[1, 9, 25, 49, 81, 1, 9, 25, 49, 81]

event_squares=[]

for x in range(10):
    if not x%2:# means not True=False;0%2=0(False),2%2=0(False) 
        event_squares.append(x*x)

print(event_squares)

output=[0, 4, 16, 36, 64]

#list comprehension way 
event_squaes=[x*x for x in range(10) if not x%2]

print(event_squares)

output=[0, 4, 16, 36, 64]

Can anyone explain to me what does the "if not x%2:" mean?

4 Answers4