How to spawn multiple enemies in pygame

Question

So im trying to make a game where the character should dodge enemies which are randomly spawned from above. The problem is, I dont know how to make the Random values different without instanciating another class, which I dont want to do. Also, with Screen.fill(), the enemies wont show up since they're being overlapped by the colour every frame, and if I dont use Screen.fill(), my character would leave a trail everytime it moves. Any Suggestions?

import random

pygame.init()
Running = True
Screen = pygame.display.set_mode((800, 600))

player_img = pygame.image.load('/Users/kevinhadinata/Downloads/ufo.png')
player_updated = pygame.transform.scale(player_img,(60,60))

enemy_list = []
enemy_img = pygame.image.load('/Users/kevinhadinata/Downloads/alien.png')
SPAWNENEMY = pygame.USEREVENT
pygame.time.set_timer(SPAWNENEMY,1000)

class Player:
    def __init__(self):
        self.ypos = 540
        self.xpos = 325
        self.height = 60
        self.width = 60
        self.playerUpdated = player_updated
    def create_player(self):
        Playerss = pygame.Rect(self.xpos,self.ypos,self.height,self.width)
        pygame.draw.ellipse(Screen, (0, 0, 0), Playerss)
        Screen.blit(player_updated, (Playerss.x, Playerss.y))

sizee = random.randint(10,40)
randomX = random.randint(0,700)

class Enemy:
    def __init__(self):
            self.xval = random.randint(0,700)
            self.size = random.randint(10,40)
    def create_enemy(self):
        Enemy = pygame.Rect(self.xval, 0, self.size,self.size)
        #enemy_updated = pygame.transform.scale(enemy_img,(self.size,self.size))
        enemy_list.append(Enemy)
        pygame.draw.ellipse(Screen,(255,255,0),Enemy)

Player = Player()
Enemys = Enemy()

while Running:
    Screen.fill((0,0,0))
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            Running = False
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                Player.xpos -= 20
            if event.key == pygame.K_RIGHT:
                Player.xpos += 20
        if event.type == SPAWNENEMY:
            Enemys.create_enemy()

    Player.create_player()

    pygame.display.update()

Answer 1

It's a good idea to not instantiate a new enemy, because just recycling it back to the top of the screen is enough. This amounts to simply changing the size & x,y.

Some of your code is occluding the Enemy class name with an Enemy variable name. I've changed this variable name to new_enemy.

class Enemy:
    def __init__(self):
        self.recycle()   # set the position & size initially

    def recycle( self ):
        # start or re-start an enemy position
        self.size = random.randint(10,40)
        self.xval = random.randint(0,700)
        self.yval = -self.size              # off the screen-top
        self.rect = pygame.Rect( self.xval, self.yval, self.size, self.size )

    def draw( self, screen ):
        pygame.draw.ellipse( screen, (255,255,0), self.rect )

    def create_enemy(self):
        global enemy_list
        new_enemy = Enemy()               # create a new Enemy
        enemy_list.append( new_enemy )    # add it to the list
    

Then in your main loop, you can recycle() any Enemy that goes off-screen.

[...]    # in main loop

# draw all the enemies, and re-position any enemies that moved off the screen
for enemy in enemy_list:
    enemy.draw( screen )
    if ( enemy.ypos > 600 ):          # TODO - don't use a fixed size
        enemy.recycle()               # move back to top

The drawing an spawning code was mixed-up, I have re-arranged this into a separate .draw() function. Using this solves the problem with clearing the screen too. Each frame, the code clears the screen, then repaints all the items.

Answer 2

You need to create a list of enemies and iterate the list in the main loop to draw each enemy. Use randint to randomly place the enemies.

Try this code:

import random, pygame

pygame.init()
Running = True
Screen = pygame.display.set_mode((800, 600))

player_img = pygame.image.load('/Users/kevinhadinata/Downloads/ufo.png')
player_updated = pygame.transform.scale(player_img,(60,60))

enemy_list = []
enemy_img = pygame.image.load('/Users/kevinhadinata/Downloads/alien.png')
SPAWNENEMY = pygame.USEREVENT
pygame.time.set_timer(SPAWNENEMY,1000)

class Player:
    def __init__(self):
        self.ypos = 540
        self.xpos = 325
        self.height = 60
        self.width = 60
        self.playerUpdated = player_updated
    def create_player(self):
        self.Playerss = pygame.Rect(self.xpos,self.ypos,self.height,self.width)
        pygame.draw.ellipse(Screen, (0, 0, 0), self.Playerss)
        Screen.blit(player_updated, (self.Playerss.x, self.Playerss.y))
        
    def draw(self):  # draw player
        Screen.blit(player_updated, (self.xpos,self.ypos))

sizee = random.randint(10,40)
randomX = random.randint(0,700)

class Enemys:
    def __init__(self):
            #self.xval = random.randint(0,700)
            self.size = random.randint(10,40)
    def create_enemy(self):
        Enemy = pygame.Rect(random.randint(100,700), 0, self.size,self.size)
        #enemy_updated = pygame.transform.scale(enemy_img,(self.size,self.size))
        enemy_list.append(Enemy)
        pygame.draw.ellipse(Screen,(255,255,0),Enemy)
        
    def draw(self):  # draw all enemies
        for e in enemy_list:
            pygame.draw.ellipse(Screen,(255,255,0),e)
            

Player = Player()  # player object
Enemys = Enemys()  # collection of enemies
Player.create_player()

while Running:
    Screen.fill((0,0,0))
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            Running = False
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                Player.xpos -= 20
            if event.key == pygame.K_RIGHT:
                Player.xpos += 20
        if event.type == SPAWNENEMY:
            Enemys.create_enemy()

    Player.draw()  # draw player
    Enemys.draw()  # draw all enemies
    pygame.display.update()