x = a + 1   # a is not yet defined

a = x + 1

class A:
    def __init__(self, rarely_used_parameter=False):
        if rarely_used_parameter:
            self.m += 1  # the member 'm' is not yet initialised, but if the testing happens to never set the 'rarely_used_parameter' to True, this error may go undetected
        self.m = 0
    def inc(self):
        self.m += self.n  # A does not have a member named 'n'.
    def init_x(self):
        self.x = 5  # any member variables should be defined in the init method
    def use_x(self):
        self.x += 1  # this will cause an error if init_x is not called beforehand