pygame position error - pygame

Question

First of all ,I loaded a picture of the ship and initialized its location. thereafter I add bullet to my program. After that, I found that no matter how I debug it, it can't be in the right place.
# 1. - import library
import pygame,sys
from pygame.locals import *
from pygame.sprite import Sprite
class Player(Sprite):
def __init__(self):
super().__init__()
self.image = pygame.image.load('image/pig.bmp')
self.rect = self.image.get_rect()
self.screen_rect = screen.get_rect()
class Bullet(Sprite):
def __init__(self, player):
super().__init__()
self.rect = pygame.Rect(0, 0, bullet_width, bullet_height )
self.color = bullet_color
self.rect.center = player.rect.center
self.rect.left = player.rect.right
# 2. - Initialize the game
pygame.init()
width,height = 800,600
screen = pygame.display.set_mode((width,height))
keys = [False,False,False,False]
playerpos = [0,288]
bullet_width = 15
bullet_height = 6
bullet_color = (200, 200 , 0)
player = Player()
bullet = Bullet(player)
grass = pygame.image.load("image/bg.bmp")
# 4. - keep looping through
while True:
# 5. - clear the screen before drawing it again.
screen.fill(0)
# 6. - Draw the screen elements.
screen.blit(grass,(0,0))
screen.blit(player.image, playerpos)
pygame.draw.rect(screen, bullet.color, bullet.rect)
# 7. - update the screen
pygame.display.flip()
# 8. - loop through the events
for event in pygame.event.get():
# check if the event is the X button.
if event.type == pygame.QUIT:
pygame.quit()
sys.exit()
and why bullet appear in top-left
enter image description here
I hope bullet appear in ship's right side,but I can't do it if I don't use coordinate（x，y），how can I do it?

Answer 1

You are drawing the ship in a position unrelated to its rect's position, using playerpos. You need to make the link the ship's position linked to its rect, so that the bullet can access it:
# 1. - import library
import pygame,sys
from pygame.locals import *
from pygame.sprite import Sprite
class Player(Sprite):
def __init__(self):
super().__init__()
self.image = pygame.image.load('image/pig.bmp')
self.image.fill((255, 0, 0))
self.rect = self.image.get_rect()
self.screen_rect = screen.get_rect()
class Bullet(Sprite):
def __init__(self, player):
super().__init__()
self.rect = pygame.Rect(0, 0, bullet_width, bullet_height )
self.color = bullet_color
self.rect.center = player.rect.center
self.rect.left = player.rect.right
# 2. - Initialize the game
pygame.init()
width,height = 800,600
screen = pygame.display.set_mode((width,height))
keys = [False,False,False,False]
bullet_width = 15
bullet_height = 6
bullet_color = (200, 200 , 0)
player = Player()
player.rect.topleft = [0,288]
bullet = Bullet(player)
grass = pygame.image.load("image/bg.bmp")
# 4. - keep looping through
while True:
# 5. - clear the screen before drawing it again.
screen.blit(grass, (0, 0))
# 6. - Draw the screen elements.
screen.blit(player.image, player.rect.topleft)
pygame.draw.rect(screen, bullet.color, bullet.rect)
# 7. - update the screen
pygame.display.flip()
# 8. - loop through the events
for event in pygame.event.get():
# check if the event is the X button.
if event.type == pygame.QUIT:
pygame.quit()
sys.exit()
This is because a surface's get_rect() method has no idea where the surface is going to be blitted on to another surface, so it just gives its position as (0, 0). get_rect() is only useful for obtaining a surface's dimensions.