如何增加点后的位数？

Question

我试图编写一个计算任意数字的立方根的代码

cube = int(input("Please Enter the number : "))
root = 0.0
tries = 0
add = 1
positive = True


while root ** 3 < cube or root ** 3 > cube :
    if root ** 3 < cube :
        if positive == True :
            root += add
            tries += 1
        elif positive == False :
            positive = True
            add = add/10
            tries += 1
    elif root ** 3 > cube :
        if positive == True :
            positive = False
            add = add/10
            tries += 1
        elif positive == False :
            root -= add
            tries += 1

print("The root is " + str(root) + ", Tries : " + str(tries)) 

当我转到http://www.pythontutor.com/live.html并尝试调试代码时，我看到如果我将值11分配给＆＃39; cube＆＃39;例如，（在步骤227中）当我决定添加＆＃39; （即0.0001）由10变为0.为什么?? !!