Why is 'True == not False' a syntax error in Python?

Question

Comparing boolean values with == works in Python. But when I apply the boolean not operator, the result is a syntax error:

Python 2         


        

Answer 1

It's just a matter of operator precedence. Try:

>>> True == (not False)
True

Have a look in this table of operator precedences, you'll find that == binds tigher than not, and thus True == not False is parsed as (True == not) False which is clearly an error.

Answer 2

It has to do with operator precedence in Python (the interpreter thinks you're comparing True to not, since == has a higher precedence than not). You need some parentheses to clarify the order of operations:

True == (not False)

In general, you can't use not on the right side of a comparison without parentheses. However, I can't think of a situation in which you'd ever need to use a not on the right side of a comparison.

Answer 3

I think what you are looking for is "and not". This gives you the results you are looking towards. If your comparing booleans what you have is a compound boolean expression, here is an example website Compound Boolean Expression.

>>> True and True
True
>>> True and not True
False
>>> True and not False
True
>>> False and not True
False
>>> False and not False
False
>>> False and False
False