Thread by @swapnakpanda

💡 Why is below expression in Python evaluated to "True"?

→→ not False == True is not True == True ←←

Originally Asked By: @DataIlm

I will try to answer this one in the easiest possible way.

🧵 👇

2 important things we need to understand while solving this one.

1️⃣ Operator Precedence
2️⃣ Operator Associativity

1️⃣ Operator Precedence

✪ Logical 'not' operator has "lower precedence" than Comparison Operators (here '==') and Identity Operators (here 'is not').

✪ Comparison Operators and Identity Operators have same precedence.

2️⃣ Operator Associativity

✪ Associativity is the order in which an expression is evaluated that has "multiple operators of the same precedence".

✪ Almost all the operators have left-to-right associativity (well almost, but not all).

Example:

5 * 4 // 3

✪ Here * and // have equal precedence. And they have left to right associativity.

So,

5 * 4 // 3 ⇨ (5 * 4) // 3 ⇨ 20 // 3 ⇨ 6

2️⃣.1️⃣ Operator Associativity for Comparison and Identity Operators

When I said, "almost all the operators have left-to-right associativity", that "almost" doesn't include Comparison, Identity and Membership operators.

So, are they right to left associative? No.

Then?

They are not associative at all. Huhhh...

Then, how do they get evaluated?

Example:

→ x < y < z

It is evaluated as

→ (x < y) and (y < z)

Cool 😎

3️⃣ Let's work

Our Original expression is

→ not False == True is not True == True

Here

✪ '==' , 'is not' and '==' all have equal precedence

✪ 'not' has the lowest precedence

not False == True is not True == True
⇩
not (False == True is not True == True)
⇩
not ((False == True) and (True is not True) and (True == True))
⇩
not (((False == True) and (True is not True)) and (True == True)) ['and' and 'and' are left to right associativity]
⇩

not (((False) and (False)) and (True))
⇩
not ((False and False) and True)
⇩
not (False and True)
⇩
not (False)
⇩
True

Hope, you found it interesting yet, easy to solve.

Original people who were in that question are:

@IAyeshaSahar @JanaSunrise @pritkalariya @aahiknsv @KuchBhiKaran @marioarrioladev

Also many thinks “is not” is combination of 2 operators “is” and “not”. But No. “is not” is a single operator.

“is” and “is not” are called Identity Operators in Python.