How to change value to zero but not in the first iteration of a loop

user_10854561 0
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I am trying to implement turning of front wheels in PyBox2D, for now, I was able to make it turn left/right but I am not able to stop it when the angle reaches zero (to make the car to go straight)

My goal is to stop turning when the angle of a wheel reaches zero or value similar to zero, but not on the beginning (sometimes when the angles are zero they do not move at all, and if possible I would like to make it independent from pressing key on a keyboard (moving those two nested if statements out of the if keyboard_is_pressed(hotkey) part did not help

I hope I made myself clear and thank you very much for any help

EDIT I tried to implement solution given in the answer, it kind of worked but I tried to improve it and now I am stuck again, the wheels turn, but when they return to their initial position they stop moving. One of problems can be that when I press "a" or "d" key my variable self.ticking changes by more than just one, because I am not able to press the key for such a short period of time.

variable self.on_the_beginning is equivalent to on_starting_race from the answer below:

    def control(self): # This makes control independent from visualisation
        #Front left suspension: index 2
        #Front right suspension: index 3
        print(self.ticking)
        if keyboard.is_pressed("a"):
            self.suspensions[2].motorSpeed = -5
            self.suspensions[3].motorSpeed = -5
            self.ticking -= 1 


        if keyboard.is_pressed("d"):                
            self.suspensions[2].motorSpeed = 5
            self.suspensions[3].motorSpeed = 5
            self.ticking += 1


        if self.ticking <= -3:
            self.ticking = -3
            self.on_the_beginning = True

        elif self.ticking >= 3:
            self.ticking = 3
            self.on_the_beginning = True

        if np.radians(-5) <= self.tires[2].wheel.angle  <= np.radians(5) and self.on_the_beginning == True and self.ticking !=0:
            self.suspensions[2].motorSpeed = 0
            self.suspensions[3].motorSpeed = 0
            self.tires[2].SetAngularVelocity = 0
            self.tires[3].SetAngularVelocity = 0
            self.ticking = 0
            on_the_beginning = False
box2d if-statement python
2 Answers

If i understand correctly, you can have a variable, say on_starting_race, set to false, then check whenever it is above a set number (say, when it's above 10 you know for a fact that the race has already started and the car moved at least for a few seconds), then change that value to True, now add an if statement to determine whether the value is close to 0 (say val<5) AND on_starting_race is True. There might be a more elegant way, but this is pretty straight forward(assuming you check the state of the car every frame or a set period of time).

user_104745660

Sorry, because I am not 100% sure of your problem without the whole code.

I think the solution could be using an input parameter in you function, let's say first_run, that you can control from inside and outside the function. 

def control(self, first_run=True):

This way, you may start the race (from your main program) setting first_run to True, so you don't care about the angle. And use this same function setting first_run to False the rest of the times.

You can also use a self.first_run variable that you may set to True in the init, then setting self.first_run to False if it is True (which is really the first time you use your control() function).

user_112979580
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