程序提供了一个简单的类来模拟弹丸的飞行

Question

我试图写一个程序，它代表了一个简单的类来模拟弹丸的飞行，并返回最大高度和旅行距离。到目前为止，我掌握的情况如下：

th import sin, cos, radians

class Projectile:
    """Simulates the flight of  simple projectiles near the eath's surface, ignoring 
wind resisitance.  Tracking is done in two dimensions, height(y) and distance(x)."""

    def __init__(self, angle, velocity, height):
        """Create a projectile with given launch angle, initial velocity and height."""

        self.xpos = 0.0
        self.ypos = height
        theta = radians(angle)
        self.xvel = velocity * cos(theta)
        self.yvel = velocity * sin(theta)

        #Find time to reach projectiles max height.
        self.th = self.yvel/9.8

    def update(self, time):
        """Update the stat of this projectile to move in time seconds farther into its flight"""

        self.xpos = self.xpos + time * self.xvel
        yvel1 = self.yvel - 9.8 * time
        self.ypos = self.ypos + time * (self.yvel + yvel1) / 2.0
        self.yvel = yvel1
        self.maxpos = max(self.maxypos, self.ypos)

    def getY(self):
        """Returns the y position (height) of this projectile."""

        return self.ypos

    def getX(self):
        """Returns the x position (distance) of this projectile."""

        return self.xpos

    def getMaxHeight(self):
        """Returns the max height of the projectile."""

        return self.maxypos

    def getInputs():
        a = eval(input("Enter the launch angle (in degrees): "))
        v = eval(input("Enter the inital velocity (in meters/sec): "))
        h = eval(input("Enter the inital height (in meters): "))
        t = eval(input("Enter the time interval between position calculations:"))
        return a, v, h, t

def main():
    angle, vel, h0, time = getInputs() 
    elapsedTime = 0.0
    cball = Projectile(angle, vel, h0)
    cball.getInputs()
    while cball.getY() >= 0:
        cball.update(time)
        elapsedTime + time
    print("\nDistance traveled: {0:0.1f} meters.".format(cball.getX()),
          " in {0:0.1f} seconds.".format(elapsedTime))
    print("\nMaximum height traveled: {0:0.1f} meters.".format(cball.getMaxY()))

if __name__ == "__main__":
    main()

但是，main（）中缺少了一些东西，因为它一直告诉我“getInputs”没有定义，而且我一辈子都搞不清楚。任何帮助都将不胜感激。你知道吗

Answer 1

在getInputs中缺少作为参数的self。应该是的

def getInputs(self)

然后你可以用cball来调用它。你知道吗

编辑：以上建议将使cball.getInputs()起作用。你知道吗

但正如注释中提到的，另一种解决方案是将getInputs（）从Projective类中移出，在这种情况下，您不会将'self'作为参数传递。你知道吗

Answer 2

更正缩进后，它就可以工作了；此时，getInputs（）函数的缩进方式可能会将其定位到类中。
行cball.getInputs()是冗余的。
eval对用户原始输入不是一个好主意，可以执行任意代码。你知道吗

一般来说，将i/o与业务逻辑结合起来不是一个好主意。您的类不应该包含i/o；将getInputs()保留为函数更好。你知道吗

from math import sin, cos, radians


class Projectile:
    """Simulates the flight of  simple projectiles near the eath's surface, ignoring
    wind resisitance.  Tracking is done in two dimensions, height(y) and distance(x)."""

    def __init__(self, angle, velocity, height):
        """Create a projectile with given launch angle, initial velocity and height."""

        self.xpos = 0.0
        self.ypos = height
        theta = radians(angle)
        self.xvel = velocity * cos(theta)
        self.yvel = velocity * sin(theta)

        #Find time to reach projectiles max height.
        self.th = self.yvel/9.8
        self.maxypos = float('-inf')

    def update(self, time):
        """Update the stat of this projectile to move in time seconds farther into its flight"""

        self.xpos = self.xpos + time * self.xvel
        yvel1 = self.yvel - 9.8 * time
        self.ypos = self.ypos + time * (self.yvel + yvel1) / 2.0
        self.yvel = yvel1
        self.maxypos = max(self.maxypos, self.ypos)

    def getY(self):
        """Returns the y position (height) of this projectile."""

        return self.ypos

    def getX(self):
        """Returns the x position (distance) of this projectile."""

        return self.xpos

    def getMaxY(self):
        """Returns the max height of the projectile."""

        return self.maxypos

def getInputs():
#     a = float(input("Enter the launch angle (in degrees): "))
#     v = float(input("Enter the inital velocity (in meters/sec): "))
#     h = float(input("Enter the inital height (in meters): "))
#     t = float(input("Enter the time interval between position calculations:"))
#     return a, v, h, t
    return 1, 2, 3, 4

def main():
    angle, vel, h0, time = getInputs() 
    elapsedTime = 0.0
    cball = Projectile(angle, vel, h0)
    while cball.getY() >= 0:
        cball.update(time)
        elapsedTime + time
    print("\nDistance traveled: {0:0.1f} meters.".format(cball.getX()),
          " in {0:0.1f} seconds.".format(elapsedTime))
    print("\nMaximum height traveled: {0:0.1f} meters.".format(cball.getMaxY()))

if __name__ == "__main__":
    main()