Python Not Operator

[ColdDigital]

Hey,

Im doing python right now on codecademy, and am on the Operator section. I understand everything so far but once I got to the Not operators I somewhat lost the understanding.

Basically its asking me if these are not true (false) or not false (true), are these answers correct?

bool_one = not True  -- False

bool_two = not 3**4 < 4**3  -- False , 81 is greater than 64 

bool_three = not 10 % 3 <= 10 % 2 --  True, 3 remainder 1 is not equal to or less than 5

bool_four = not 3**2 + 4**2 != 5**2 False, 25 is equal to 25

bool_five =  not not False -- wt* does this mean? 

Thanks

[werto165]

4 minutes ago, ColdDigital said:

bool_five =  not not False -- wt* does this mean?

false I assume. double negative, I'm not 100% sure tho I've never really done this stuff before. 

[Enderman]

1 is right

2 is actually true, because (3**4 < 4**3) returns false, and "not" reverses that 

3 and 4 you can probably solve by yourself based on what i said about 2

5 if not false is true, then not not false would be _______

i think thats how it works, i havent done python for a few years...

[spenser_l]

You can think of it like this:

not (not False) = not (True) = False

[spenser_l]

If you're not sure about the answers, you can always just execute the program to see the results. I've done so in Java just for peace of mind and will explain each of the tests. For simplicity in Java I've just put the result of the exponent parts.

public class Test {

	public static void main(String[] args) {
		
		boolean test[] = new boolean[5];
		
		test[0] = !true;
	
		test[1] = !(81 < 64);
		
		test[2] = !(10 % 3 <= 10 % 2);
		
		test[3] = !((9 + 16) != 25);
		
		test[4] = !!false;
		
		for (boolean b : test) {
			System.out.println(b);
		}
		// results:
		// 1. false
		// 2. true
		// 3. true
		// 4. true
		// 5. false
	}
}

1. not True: not (or ! in Java) just means the opposite of whatever the result is, so False.

2. not (81 < 64): 81 is NOT less than 64, so that expression results in False. So not False is True.

3. not (10 % 3 <= 10 % 2): 10 mod 3  = 1, 10 mod 2 = 0. So 1 <= 0 is False, and not False is True.

4. not ((9 + 16) != 25): 9 + 16 = 25 != 25. Well 25 IS equal to 25, so the expression is False, and not False is True.

5. not not False: again, think of it like this: not (not False) = not True = False.

Feel free to ask if any of this is unclear.

[ColdDigital]

26 minutes ago, Enderman said:

1 is right

2 is actually true, because (3**4 < 4**3) returns false, and "not" reverses that 

3 and 4 you can probably solve by yourself based on what i said about 2

5 if not false is true, then not not false would be _______

i think thats how it works, i havent done python for a few years...

bool_two = not 3**4 < 4**3  -- True: 81 is not less than 64, its greater. Meaning it would be false but cause of the not its True. That how I understood it from your explanation.

bool_three = not 10 % 3 <= 10 % 2 --  3 remainder 1 is less than or equal to 5, it will take the true value being: 3 remainder 1 being less than 5. This would make it True, cause of the not it makes it false. 

bool_four = not 3**2 + 4**2 != 5**2 -- 25 is equal to 25, so its false, cause of not in front of the statement, its True. 

bool_five =  not not false, not false = True, not true  = False , so False

Edit: Nvm, messed up boolean_three, know why only asked for the remainders.

so bool_three would be true: bool_three = not 10 % 3 <= 10 % 2 --  10 % 3 has 1 remainder, 10  % 2 has 0 remainders. 1 <= 0, equals false, because of not its true, in other words not false = True

Hope its correct now. If it is thanks a bunch! Found these Not operators a complete mind f**k

[ColdDigital]

10 minutes ago, spenser_l said:

If you're not sure about the answers, you can always just execute the program to see the results. I've done so in Java just for peace of mind and will explain each of the tests. For simplicity in Java I've just put the result of the exponent parts.

public class Test {

	public static void main(String[] args) {
		
		boolean test[] = new boolean[5];
		
		test[0] = !true;
	
		test[1] = !(81 < 64);
		
		test[2] = !(10 % 3 <= 10 % 2);
		
		test[3] = !((9 + 16) != 25);
		
		test[4] = !!false;
		
		for (boolean b : test) {
			System.out.println(b);
		}
		// results:
		// 1. false
		// 2. true
		// 3. true
		// 4. true
		// 5. false
	}
}

1. not True: not (or ! in Java) just means the opposite of whatever the result is, so False.

2. not (81 < 64): 81 is NOT less than 64, so that expression results in False. So not False is True.

3. not (10 % 3 <= 10 % 2): 10 mod 3  = 1, 10 mod 2 = 0. So 1 <= 0 is False, and not False is True.

4. not ((9 + 16) != 25): 9 + 16 = 25 != 25. Well 25 IS equal to 25, so the expression is False, and not False is True.

5. not not False: again, think of it like this: not (not False) = not True = False.

Feel free to ask if any of this is unclear.

I see what I did wrong on number 3, I did the whole division, it asked me instead to only solve how many remainders would be left in each expression. Its clear now after I looked at your java comment, thanks man appreciate your help!

[madknight3]

It helps to understand operator precedence (link to the Python docs).

Let's apply operator precedence to one of the questions

bool_two = not 3**4 < 4**3

So according to the order of operations, exponentiation is applied first.

bool_two = not 81 < 64

So we only have two operations left. The less than, and the not. The less than operator gets applied next.

bool_two = not False

And finally the not operator is applied.

bool_two = True