[FIXED] how light works traffic simulation in python

Issue

I'm trying to build a light for traffic simulation system I'm writing a light class which is represents a traffic signal like this

• 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. Like this pic:it shows how the light works

so I wrote this

class Light:
    """Represents a traffic light"""

    def __init__(self, period, green_period):
        self.period = period
        self.green_period = green_period
        self.color = 'G'

    def __str__(self):
        return self.color

    def __repr__(self):
        pass

    def step(self):
        time = 0
        while True:
            time += 1
            if time < self.green_period:
                self.color = 'G'
            else:
                self.color = 'R'
            if time == self.green_period:
                break

    def is_green(self):
        if self.color == 'G':
            return True
        elif self.color == 'R':
            return False


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()

def main():
    """Demonstrates the classes"""
    print('\nLight demonstration\n')
    demo_light()


if __name__ == '__main__':
    main()

I'm trying to get this

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

but the result is:

0 G True
1 R False
2 R False
3 R False
4 R False
5 R False
6 R False
7 R False
8 R False
9 R False
10 R False
11 R False
12 R False
13 R False
14 R False

Solution

def step(self):
    time = 0
    while True:
        time += 1
        if time < self.green_period:
            self.color = 'G'
        else:
            self.color = 'R'
        if time == self.green_period:
            break

So, this is the Light::step function, and what we know is that the problem comes from here, since it's supposed to turn the light from green to red, but it seems to always give red.

a_light = Light(7, 3)

This is our instance of Light, it has a period of 7 and a green_period of 3.

The image above is how you explained it's supposed to work.

---

The problem is in the first line of the method step, because time is always set to zero, and so the value "returned" (there's no return but I think you got it) will be always the same since the only "variable" always starts from the same value.

def __init__(self, period, green_period):
    self.period = period
    self.green_period = green_period
    self.color = 'G'
    self.time = 0 # This variable will tell you which instant we're in

Now that you have time as a variable attribute, you can re-write the step function this way.

def step(self):
    self.time += 1
    # If time is on green phase...
    if time%self.period < self.green_period: # [For example 9%7 < 3]
        # ...then turn it to green (doesn't matter if it's already green)
        self.color = 'G'
    else: # ...else, if the time isn't on green phase it must be on red phase
        self.color = 'R'

This should work, I haven't tested it but I think it's very close to what you need.

Answered By - FLAK-ZOSO