import abc


class State(object, metaclass=abc.ABCMeta):
    def __init__(self):
        self.color_index = 0

    @abc.abstractmethod
    def light(self):
        COLORS = ["Green", "Red", "Blue", "Yellow"]
        state_color = COLORS[self.color_index]
        self.color_index += 1
        if self.color_index == len(COLORS):
            self.color_index = 0
        return state_color


class Lamp(State):
    def __init__(self):
        super().__init__()
        self.color = None

    def light(self):
        self.color = super().light()
        return self.color


if __name__ == '__main__':
    # These "asserts" using only for self-checking and not necessary for auto-testing

    lamp_1 = Lamp()
    lamp_2 = Lamp()

    lamp_1.light()  # Green
    lamp_1.light()  # Red
    lamp_2.light()  # Green

    assert lamp_1.light() == "Blue"
    assert lamp_1.light() == "Yellow"
    assert lamp_1.light() == "Green"
    assert lamp_2.light() == "Red"
    assert lamp_2.light() == "Blue"
    print("Coding complete? Let's try tests!")