STATE_VAR = 0

def do_something(arg1):
    global STATE_VAR
    if arg1:
        STATE_VAR = 1

def say_hello():
    if STATE_VAR:
        print("Hello!")

class MyClass:
    STATE_VAR = 0

    @classmethod
    def do_something(cls, arg1):
        if arg1:
            cls.STATE_VAR = 1

    @classmethod
    def say_hello(cls):
        if cls.STATE_VAR:
            print("Hello!")