Python - Why without parentheses is False?

Question

arr = [1, True, 'a', 2]
print('a' in arr)
print('a' in arr in arr)
print(('a' in arr) in arr)

Answer 1

'a' in arr in arr
== ('a' in arr) and (arr in arr)
== (True) and (False)
== False.

"Formally, if a, b, c, …, y, z are expressions and op1, op2, …, opN are comparison operators, then (a op1 b op2 c ... y opN z) is equivalent to (a op1 b and b op2 c and ... y opN z), except that each expression is evaluated at most once".
https://docs.python.org/3/reference/expressions.html#comparisons

Answer 2

I think in is evaluated from right to left.

Answer 3

python 2 used to work without parentheses, but in python 3 y need to separate your code using parentheses