Python - Why doesn't --a raise an error, but neither change "a" value?

Question

a = 5
b = 7
if not a != b - 2:
print("a =",a)
print("b =",b)
b = --a
print("a =",a)
print(a + b)

Answer 1

It is just a double negation :

- - a = - 1 * -1 * a

So the only thing u r doing is setting b=a.

Answer 2

I understand now! Thank you!