每次终止一个敌人时都会添加一个新敌人

Question

简而言之，我想在每一次消灭敌人时增加一个敌人。我用有限的知识尝试了几种不同的方法，还尝试通过搜索引擎找到类似的解决方案。

由于舰船和敌人的图像不在当前目录中，因此它们不会出现。

这是我所说的游戏代码：

#Among the Stars
#Set up the screen

import turtle, os, math, random, time
#import os
#import math
#import random
#import time

#Set up the screen
wn = turtle.Screen()
wn.bgcolor("black")
wn.title("Among the Stars")
wn.bgpic("outinspace.gif")

#Register the shapes
turtle.register_shape("enemy.gif")
turtle.register_shape("player.gif")

#Draw border
border_pen = turtle.Turtle()
border_pen.speed(0)
border_pen.color("white")
border_pen.penup()
border_pen.setposition(-300, -300)
border_pen.pendown()
border_pen.pensize(3)
for side in range(4):
    border_pen.fd(600)
    border_pen.lt(90)
border_pen.hideturtle()

#Set the score to 0
score = 0

#Draw the score
score_pen = turtle.Turtle()
score_pen.speed(0)
score_pen.color("white")
score_pen.penup()
score_pen.setposition(-290, 280)
scorestring = "Score: %s" %score
score_pen.write(scorestring, False, align="left", font=("Arial", 14, "normal"))
score_pen.hideturtle()

#Create the player turtle
player = turtle.Turtle()
player.color("blue")
player.shape("player.gif")
player.penup()
player.speed(0)
player.setposition(0, -250)
player.setheading(90)
#turtle.tracer(10, 10)

playerspeed = 20

#Choose a number of enemies
number_of_enemies = 10
#Create an empty list of enemies
enemies = []

#Add enemies to the list
for i in range(number_of_enemies):
    #Create the enemy
    enemies.append(turtle.Turtle())

for enemy in enemies:
    enemy.color("red")
    enemy.shape("enemy.gif")
    enemy.penup()
    enemy.speed(0)
    x = random.randint(-200, 200)
    y = random.randint(100, 250)
    enemy.setposition(x, y)

enemyspeed = 2

#Create the player's bullet
bullet = turtle.Turtle()
bullet.color("yellow")
bullet. shape("triangle")
bullet.penup()
bullet.speed(0)
bullet.setheading(90)
bullet.shapesize(0.5, 0.5)
bullet.hideturtle()
turtle.tracer(10, 10)

bulletspeed = 20

#Define bullet state
#ready - ready to fire
#fire - bullet is firing
bulletstate = "ready"

#Move the player left and right
def move_left():
    x = player.xcor()
    x -= playerspeed
    if x < -280:
        x = - 280
    player.setx(x)

def move_right():
    x = player.xcor()
    x += playerspeed
    if x > 280:
        x = 280
    player.setx(x)

def fire_bullet():
    #Declare bulletstate as a global if it needs changed
    global bulletstate
    if bulletstate == "ready":
        os.system("afplay laser.wav&")
        bulletstate = "fire"
        #Move the bullet to just above the player
        x = player.xcor()
        y = player.ycor() + 10
        bullet.setposition(x, y)
        bullet.showturtle()

def isCollision (t1, t2):
    distance = math.sqrt(math.pow(t1.xcor()-t2.xcor(),2)+math.pow(t1.ycor()-t2.ycor(),2))
    if distance < 25:
        return True
    else:
        return False


#Create keyboard bindings
turtle.listen()
turtle.onkey(move_left, "Left")
turtle.onkey(move_right, "Right")
turtle.onkey(fire_bullet, "space")

#Main game loop
while True:

    for enemy in enemies:
        #Move the enemy
        x = enemy.xcor()
        x += enemyspeed
        enemy.setx(x)

        #Move the enemy back and down
        if enemy.xcor() > 280:
            #Move all enemies down
            for e in enemies:
                y = e.ycor()
                y -= 20
                e.sety(y)
            #Change enemy direction
            enemyspeed *= -1

        if enemy.xcor() < -280:
            #Move all enemies down
            for e in enemies:
                y = e.ycor()
                y -= 20
                e.sety(y)
            #Change enemy direction
            enemyspeed *= -1

        #Check for a collision between the bullet and the enemy
        if isCollision(bullet, enemy):
            os.system("afplay explode.wav&")
            #Reset the bullet
            bullet.hideturtle()
            bulletstate = "ready"
            bullet.setposition(0, -400)
            #Reset the enemy
            x = random.randint(-200, 200)
            y = random.randint(100, 250)
            enemy.setposition(x, y)
            #Add another enemy

            #Update the score
            score += 10
            scorestring = "Score: %s" %score
            score_pen.clear()
            score_pen.write(scorestring, False, align="left", font=("Arial", 14, "normal"))

        if isCollision(player, enemy):
            os.system("afplay explode.wav&")
            player.hideturtle()
            enemy.hideturtle()
            print ("Game Over")
            break

    #Move the bullet
    if bulletstate == "fire":
        y = bullet.ycor()
        y += bulletspeed
        bullet.sety(y)

    #Check to see if the bullet has gone to the top
    if bullet.ycor() > 275:
        bullet.hideturtle()
        bulletstate = "ready"



delay = input("Press enter to finish.")