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pythonbooleanboolean-logic
Cheong Wai Hong
Cheong Wai Hong

Reputation: 19

Python 'not' operator

x = 0

if not x:
    print(bool(x))
    print("Evaluated True")

else:
    print(bool(x))
    print("Evaluated False")

Output 

False
Evaluated True

Why is the else block not executed? I think x = 0 is False, not x is True. Or do I misunderstand the boolean definition?

Upvotes: 0

Views: 334

Answers (7)

joshijai2
joshijai2

Reputation: 177

False
Evaluated True

Your output is correct. You got the boolean concept right(x = 0 is False, not x is True) but your implementation is wrong.

x = 0

if not x:
    print(bool(x))
    print("Evaluated True")

In your code:

if not x means if (not x)==True which is absolutely correct hence the if condition runs.

Using if (some condition) is sometimes tricky. Its also sometimes due to absence of parentheses.

You can achieve the desired output with this if (not x)==False.

Upvotes: 1

new Q Open Wid
new Q Open Wid

Reputation: 2313

The boolean value is true for all except 0. not x == True so it's evaluated true.

Upvotes: 1

mohammed wazeem
mohammed wazeem

Reputation: 1328

>>> x = 0
>>> if x:
...   print(bool(x), "Evaluated True")
... else:
...   print(bool(x),"Evaluated False")
... 
False Evaluated False

Note: The boolean value is True for all integers except 0

Upvotes: 2

Chrissu
Chrissu

Reputation: 417

if not x

This is true, that's why the line following the if is executed. Ergo, the else is NOT executed. It would only be executed if the if statement would be false.

Upvotes: 1

Mace
Mace

Reputation: 1410

You must print your if expression 'not x'. Then you see not x == not False == True.

x = 0

if not x:
    print(bool(not x))
    print("Evaluated True")

else:
    print(bool(not x))
    print("Evaluated False")

answer:

True
Evaluated True

Upvotes: 2

Alexander
Alexander

Reputation: 188

Thus it as you say: not x == True so the if statement get executed.

Upvotes: 1

Mahmood Darwish
Mahmood Darwish

Reputation: 546

When the expression inside the if statement is true the if block is executed. Since x is 0 then not x is true which means the if block will execute not the else block.

print(bool(x)) will print false since x is 0.

Upvotes: 1

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