python - 如何将值更改为零，而不是在循环的第一次迭代中更改(How to change value to zero but not in the first iteration of a loop)

Question

The bounty expires in 7 days) . 赏金将 在7天后过期) 。) Answers to this question are eligible for a +50 reputation bounty. 这个问题的答案有资格获得+50声望奖励。) Mechatrnk is looking for an up-to-date answer) to this question: I need to be able to align my car wheels so the car can move straight, but under given circumstances, the car wheels can only turn from left to right, they very scarcely stop when their angle is zero, so the car cannot drive straight Mechatrnk正在寻找该问题的最新答案) ：我需要能够对齐我的车轮，以便汽车可以直行，但是在特定情况下，车轮只能从左向右旋转，它们非常当它们的角度为零时几乎不会停止，因此汽车无法直行)

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)

(我正在尝试在PyBox2D中实现前轮的转向，目前，我能够使其左转/右转，但是当角度达到零时我无法将其停止（以使汽车直行）)

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

(我的目标是在轮子的角度达到零或近似于零的值时停止转弯，但不要在一开始就停止转动（有时，当角度为零时，它们根本不会移动，如果可能，我想使其独立于按下键盘上的键（将这两个嵌套的if语句移出if keyboard_is_pressed（hotkey）部分没有帮助)

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

(我希望我能说清楚一点，非常感谢您的帮助)

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.

(编辑我尝试实施答案中给出的解决方案，虽然可行，但我尝试进行改进，现在又卡住了，车轮转动了，但是当它们返回初始位置时，它们停止了运动。)

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.

(问题之一可能是，当我按下“ a”或“ d”键时，我的变量self.ticking改变的幅度不止一个，因为我无法在这么短的时间内按下该键。)

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

(变量self.on_the_beginning等效于以下答案中的on_starting_race：)

    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

  ask by Mechatrnk translate from so

Answer 1

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.

(如果我理解正确，则可以将变量on_starting_race设置为false，然后检查它是否超过设置的数字（例如，当它超过10时，您就知道比赛已经开始并且汽车行驶在至少几秒钟），然后将该值更改为True，现在添加一个if语句以确定该值是否接近0（例如val <5）并且on_starting_race为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).

(可能有一种更优雅的方法，但这很简单（假设您每隔一帧或在设定的时间段内检查汽车的状态）。)