遇到“NameError”问题

Question

我是新的课程，这是我第三次尝试做一个。我遇到了一个 NameError ，我真的不知道如何解决。看看我的程序，看看你能不能帮忙。

import random
import math
import pygame
import pickle 

# initialise pygame
pygame.init()

# player class 
class player(object):
    def __init__(self, playerimage, playerX, playerY = 700, playerX_change = 0):
        self.playerimage = pygame.image.load("Main Player.png") 
        self.playerX = 365
        self.playerY = 700 
        self.playerX_change = 0 

# laser class 
# ready - bullet not on screen
# fire - bullet is shown on screen and is moving

class laser(object):
    def __init__(self, laserimage, laserX, laserY, laserY_change):
        self.laserimage = pygame.image.load("laser.png")
        self.laserX = 0
        self.laserY = 700 
        self.laserY_change = 10
        self.laser_state = "ready"

# alien player / random movement = random.randint()
class alien(object):
    def __init__(self, alienimage, alienX, alienY, alienX_change, alienY_change, amount_aliens):
        self.alienimage = pygame.image.load("alien.png")
        self.alienX = []
        self.alienY = []
        self.alienX_change = []
        self.alienY_change = []
        self.amount_aliens = 10

    for i in range(ufo.amount_aliens):
        ufo.alienimage.append(pygame.image.load('alien.png'))
        ufo.alienX.append(random.randint(0, 735))
        ufo.alienY.append(random.randint(50, 200))
        ufo.alienX_change.append(3)
        ufo.alienY_change.append(7)

score = 0


# define player
def main_player(x, y):
    screen.blit(male.playerimage, (x, y))


# define laster
def fire_laser(x, y):
    lasr.laser_state = "fire"
    screen.blit(lasr.laserimage, (x + 16, y + 10))


# define alien
def alien(x, y, i):
    screen.blit(ufo.alienimage[i], (x, y))


# collision detection
def hascollision(alienX, alienY, laserX, laserY):
    distance = math.sqrt((math.pow(alienX - laserX, 2)) + (math.pow(alienY - laserY, 2)))
    if distance < 27:
        return True
    else:
        return False

#frames per second 
clock = pygame.time.Clock()

# background
background = pygame.image.load('stars.png')

# display and screen title/icon
(width, height) = (800, 800)
screen = pygame.display.set_mode((width, height))
flip = pygame.display.flip()
pygame.display.set_caption("space fighters")
pygame.event.get()
icon = pygame.image.load('logo.png')
pygame.display.set_icon(icon)

from sys import exit

ufo = alien()
lasr = laser(0, 700, 32, 32)
male = player(365, 700,)
# loop of functions
executed = True
while executed:
    screen.fill((63, 62, 63))
    # image background
    screen.blit(background, (0, 0))
    for event in pygame.event.get():
        # if key pressed, check which input, right or left?
        if event.type == pygame.KEYDOWN:
            print("key pressed")
            if event.key == pygame.K_a:
                male.playerX_change = -6
            if event.key == pygame.K_s:
                male.playerX_change = 6
        if event.type == pygame.KEYUP:
            if event.key == pygame.K_a or event.key == pygame.K_s:
                male.playerX_change = 0
            if event.key == pygame.K_SPACE:
                if lasr.laser_state is "ready":
                    lasr.laserX = male.playerX
                fire_laser(lasr.laserX, lasr.laserY)
    #frames per second is 60fps
    clock.tick(60)
    # bounrary algorithm, prevents player moving out/enemy.
    male.playerX += male.playerX_change

    if male.playerX <= 0:
        male.playerX = 0
    elif male.playerX >= 736:
        male.playerX = 736

    # boundry algorithm, make sure alien doesn't go out of bountry
    for i in range(ufo.amount_aliens):
        ufo.alienX[i] += ufo.alienX_change[i]
        if ufo.alienX[i] <= 0:
            ufo.alienX_change[i] = 4
            ufo.alienY[i] += ufo.alienY_change[i]
        elif ufo.alienX[i] >= 736:
            ufo.alienX_change[i] = -4
            ufo.alienY[i] += ufo.alienY_change[i]

    # collision
        collision = hascollision(ufo.alienX[i], ufo.alienY[i], lasr.laserX, lasr.laserY)
        if collision:
            lasr.laserY = 650
            lasr.laser_state = "ready"
            score += 5
            print(score)
            alienX[i] = random.randint(0, 735)
            alienY[i] = random.randint(50, 200)

        alien(ufo.alienX[i], ufo.alienY[i], i)

    # movement of laser shot
    if lasr.laserY <= 0:
        lasr.laserY = 650
        lasr.laser_state = "ready"

    if lasr.laser_state is "fire":
        fire_laser(lasr.laserX, lasr.laserY)
        lasr.laserY -= lasr.laserY_change

    # updates screen to show screen
    main_player(male.playerX, male.playerY)
    pygame.display.update()
pygame.quit()

这是 Visual Studio 代码给出的错误输出（在第 39 行）
对于我在范围内（ufo.amount_aliens）： NameError: name 'ufo' 未定义

Answer 1

alien 类有点混乱。 （虽然很难判断这是否只是 SO 粘贴中的缩进问题。）我将假设需要在课堂之外制作 ufos 列表，因为这是唯一有意义的事情。稍后在代码中，您声明了一个 alien 函数，该函数也将遮挡 alien 类。您需要先解决此问题 - 最好将其移入 alien 类，为 alien.draw()

所以要制作一堆外星人，创建一个列表：

alien_image = pygame.image.load('alien.png')
all_ufos = []
for i in range( amount_aliens ):
    x_pos = random.randint(  0, 735 )
    y_pos = random.randint( 50, 200 )
    x_speed = 3
    y_speed = 7
    all_ufos.append( alien( alien_image, x_pos, y_pos, x_speed, y_speed ) )

从alien 对象中删除amount_aliens，使其现在只代表一个外星人。

class alien( object ):
    def __init__( self, alienimage, alienX, alienY, alienX_change, alienY_change ):
        self.alienimage = alienimage
        self.alienX = alienX
        self.alienY = alienY
        self.alienX_change = alienX_change
        self.alienY_change = alienY_change

并将支持功能移到外星人类中。

   def draw( self, screen ):
       """ Draw the alien to the screen """
       screen.blit( self.alienimage, ( self.alienX, self.alienY ) )

   def hasCollision( self, laserX, laserY ):
       """ Has the laser at collided with this alien? """
       distance = math.sqrt((math.pow(self.alienX - laserX, 2)) + (math.pow(self.alienY - laserY, 2)))
       return ( distance < 27 ):

这允许你的主循环遍历外星人列表，简单地做stuff：

### Main Loop
while not exiting:
    ...

    # paint all UFO sprites
    for ufo in all_ufos:
        ufo.draw( screen )

    # check all lasers for collision
    for laser in all_lasers:
        for ufo in all_ufos:
            if ( ufo.hasCollision( laser.laserX, laser.laserY ) ):
                print( "*boom*" )

您在这里所做的是重新创建 PyGame Sprite 和 SpriteGroup 类的一些功能。它可能值得一个quick read of the documentation。