Class Light

The class Light represents a traffic signal.

A traffic signal is characterized by the following attributes:

• period i.e. the number of time steps between two changes from green to red
• green period i.e. the number of time steps where the signal is green.

The course of a signal with period 7 and green period 3 can be illustrated in this way:

Timestep	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
Internal clock	0	1	2	3	4	5	6	0	1	2	3	4	5	6	0	1
Color	G	G	G	R	R	R	R	G	G	G	R	R	R	R	G	G

For the sake of simplicity, we always let the signals start with the green period.

A signal thus has an internal clock that runs "circular", i.e. it starts at zero and goes to the period length after which it starts at zero again.

The class needs

• a constructor Light(period, green_period) which specifies the attributes,
• a method step() which advances the internal clock,
• a method is_green() which returns True if the signal is green, and False otherwise,and
• a __str__()-method that returns an appropriate text representation of the signal.

Note that the color does not need to be stored as an instantiated variable. That attribute is easily calculated based on the value of the green period and the value of the internal clock.

Demonstration:

Kod	Utskrift
def demo_light(): """Demonstrats the Light class""" a_light = Light(7, 3) for i in range(15): print(i, a_light, a_light.is_green()) a_light.step()	0 (G) True 1 (G) True 2 (G) True 3 (R) False 4 (R) False 5 (R) False 6 (R) False 7 (G) True 8 (G) True 9 (G) True 10 (R) False 11 (R) False 12 (R) False 13 (R) False 14 (G) True

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