Python's 'if' statement gets privileged information from conditionals

fun.py

# python 'if' statement is priviliged to the boolean output of compound conditionals
# other statements are not, and have to double-evaluate the output
# unless the output is "the last one"

class X:
    def __init__(self):
        self.v = False
        self.c = 0

    def __bool__(self):
        self.c = self.c + 1
        print("boolin'", self.c)
        self.v = not self.v
        return self.v

y = 1
n = 0

# case 1: 'if' gets a bool back from "or"
x = X()
if x or y:
    assert x.c == 1
else:
    # we never get here, because if doesnt' need to reevaluate x
    assert False

# case 2: looks like the same code as above, but z isn't priviliged like 'if'
x = X()
z = x or y

if z:
    assert False
else:
    # we had to bool twice...
    assert x.c == 2


# case 3: 'not' is not priviliged, like 'if;
x = X()
z = not(x or y)

if z:
    assert x.c == 2
else:
    assert False


# case 4: we don't need to double-evaluate this
x = X()
z = n or x

if z:
    assert x.c == 1
else:
    assert False