Pygame Character wont move left or right

Question

In my below code using PyGame, the character won't move left or right and the bullet won't shoot. I'm not sure what's causing this. It works without the whole start menu with buttons concept so I was wondering if that is the issue?

import pygame
from pygame import mixer
import math
import random
import time

# Initialize pygame module
pygame.init()

# Create the screen
screen = pygame.display.set_mode((800, 600))
display_width = 800
display_height = 600

# Background
background = pygame.image.load('space1.jpg')

# Background Sound
mixer.music.load('background.wav')
mixer.music.play(-1)

# Title and Icon
pygame.display.set_caption('Space Invaders')
icon = pygame.image.load('ufo.png')
pygame.display.set_icon(icon)

# Player
playerImg = pygame.image.load('space-invaders.png')
playerX = 370
playerY = 480
player_change = 0
playerX += player_change

# Enemy
enemyImg = []
enemyX = []
enemyY = []
enemyX_change = []
enemyY_change = []
num_of_enemies = 6

# Colours
WHITE = (255, 255, 255)
BLACK = (0, 0, 0)
RED = (150, 0, 0)
GREEN = (0, 150, 0)
BRIGHT_RED = (255, 0,0)
BRIGHT_GREEN = (0, 255, 0)


for i in range(num_of_enemies):
    enemyImg.append(pygame.image.load('alien.png'))
    enemyX.append(random.randint(0, 736))
    enemyY.append(random.randint(50, 150))
    enemyX_change.append(2)
    enemyY_change.append(40)

# Bullet

# Ready - You cant see the bullet on the screen
# Fire - The bullet is current moving
bulletImg = pygame.image.load('bullet.png')
bulletX = 0
bulletY = 480

bulletY_change = 10
bullet_state = 'ready'

# Score
score_value = 0
font = pygame.font.Font('freesansbold.ttf', 32)

textX = 10
textY = 10

# Game Over Text
over_font = pygame.font.Font('freesansbold.ttf', 64)

# Clock
clock = pygame.time.Clock()

def show_score(x, y):
    score = font.render('score : ' + str(score_value), True, (0, 255, 0))
    screen.blit(score, (x, y))

def game_over_text():
    over_text = over_font.render('GAME OVER', True, (0, 255, 0))
    screen.blit(over_text, (200, 250))

def player(x, y):
    screen.blit(playerImg, (x, y))


def enemy(x, y, i):
    screen.blit(enemyImg[i], (x, y))


def fire_bullet(x, y):
    global bullet_state
    bullet_state = 'fire'
    screen.blit(bulletImg, (x + 16, y + 10))

def isCollision(enemyX, enemyY, bulletX, bulletY):
    distance = math.sqrt((math.pow(enemyX - bulletX, 2)) + (math.pow(enemyY - bulletY, 2)))
    if distance < 27:
        return True
    else:
        return False

def text_objects(text, font):
    textSurface = font.render(text, True, WHITE)
    return textSurface, textSurface.get_rect()

def game_intro():
    intro = True

    while intro:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()
                quit()
            screen.fill(BLACK)
            largeText = pygame.font.Font('freesansbold.ttf', 105)
            TextSurf, TextRect = text_objects('Space Invaders', largeText)
            TextRect.center = ((display_width/2), 200)
            screen.blit(TextSurf, TextRect)

            button('Start Invasion', 325, 350, 150, 50, GREEN, BRIGHT_GREEN, 'play')
            button('Quit Mission', 325, 450, 150, 50, RED, BRIGHT_RED, 'quit')

            pygame.display.update()
            clock.tick(15)

#Game Loop

def game_loop(playerX, playerY, player_change, bulletX, bulletY, bulletX_change, bulletY_change, bullet_state, bulletImg):
    running = True
    while running:
        playerX = 370
        playerY = 480
        player_change = 0
        playerX += player_change

        # RGB         R    G    B
        screen.fill((0, 0, 0))
        # Background Image
        screen.blit(background, (0, 0))
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                running = False

            # If keystroke is pressed check whether its left or right
            if event.type == pygame.KEYDOWN:
                if event.key == pygame.K_LEFT:
                    player_change = -5
                if event.key == pygame.K_RIGHT:
                    player_change = 5
                if event.key == pygame.K_SPACE:
                    if bullet_state is 'ready':
                        bullet_sound = mixer.Sound('laser.wav')
                        bullet_sound.play()
                        # Get the current x coordinate of the spaceship
                        bulletX = playerX
                        fire_bullet(bulletX, bulletY)

            if event.type == pygame.KEYUP:
                if event.key == pygame.K_LEFT or event.key == pygame.K_RIGHT:
                    player_change = 0

        # boundary for spaceship
        if playerX <= 0:
            playerX = 0
        elif playerX >= 736:
            playerX = 736

        # Enemy movement
        for i in range(num_of_enemies):

            # Game Over
            if enemyY[i] > 440:
                for j in range(num_of_enemies):
                    enemyY[j] = 2000
                game_over_text()
                break

            enemyX[i] += enemyX_change[i]
            if enemyX[i] <= 0:
                enemyX_change[i] = 2
                enemyY[i] += enemyY_change[i]
            elif enemyX[i] >= 736:
                enemyX_change[i] = -2
                enemyY[i] += enemyY_change[i]
            # Collision
            collision = isCollision(enemyX[i], enemyY[i], bulletX, bulletY)
            if collision:
                explosion_sound = mixer.Sound('explosion.wav')
                explosion_sound.play()
                bulletY = 480
                bullet_state = "ready"
                score_value += 1
                enemyX[i] = random.randint(0, 736)
                enemyY[i] = random.randint(50, 150)

            enemy(enemyX[i], enemyY[i], i)

        # Bullet movement
        if bulletY <= 0:
            bulletY = 480
            bullet_state = 'ready'
        if bullet_state is 'fire':
            fire_bullet(bulletX, bulletY)
            bulletY -= bulletY_change

        player(playerX, playerY)
        show_score(textX, textY)
        pygame.display.update()

def button(msg, x, y, w, h, inactivecolour, activecolour, action=None):
    mouse = pygame.mouse.get_pos()
    click = pygame.mouse.get_pressed()
    if x + w > mouse[0] > x and y + h > mouse[1] > y:
        pygame.draw.rect(screen, activecolour, (x, y, w, h))
        if click[0] == 1 and action != None:
            if action == 'play':
                game_loop(370, 480, 0, 0, 480, 0, 10, 'ready', pygame.image.load('bullet.png'))
            if action == 'quit':
                pygame.quit()
                quit()

    else:
        pygame.draw.rect(screen, inactivecolour, (x, y, w, h))

    smallText = pygame.font.Font('freesansbold.ttf', 20)
    textSurf, textRect = text_objects(msg, smallText)
    textRect.center = ((x + (w / 2)), (y + (h / 2)))
    screen.blit(textSurf, textRect)

game_intro()

Welcome to Stack Overflow! As it stands right now, your question will be pretty hard to answer without a lot of effort on our part. Please [edit your question](https://stackoverflow.com/posts/59975317/edit) to include some additional details about your *specific* problem, highlighting any error messages or warnings you might be getting. This will make it easier to spot your bug, and thus more likely that your question gets answered. Good luck! — Das_Geek, Jan 29 '20 at 20:55
Something that will help would be stepping through your code in a debugger. This will show any weird behavior more clearly and might provide the extra details you need to include in your question. Who knows, maybe by stepping through the code yourself, you might find the solution as well! — Das_Geek, Jan 29 '20 at 20:57

Rabbid76 · Accepted Answer · 2020-01-30T17:45:58.303

the character won't move

The movement of the player player_change is continuously set 0, in the main application loop. Further more, the position of the player is continuously initialized:

def game_loop(playerX, playerY, player_change, bulletX, bulletY, bulletX_change, >bulletY_change, bullet_state, bulletImg):
   running = True
   while running:
       playerX = 370
       playerY = 480
       player_change = 0

Initialize playerX, playerY and player_change before the loop:

def game_loop(playerX, playerY, player_change, bulletX, bulletY, bulletX_change, bulletY_change, bullet_state, bulletImg):
    running = True
    player_change = 0
    playerX = 370
    playerY = 480
    while running:    
        playerX += player_change
        # [...]

the bullet won't shoot

If you want to fire a bullet, then you have to set the initial position of the bullet bulletX, bulletY = playerX, playerY and set bullet_state = 'fire':

def game_loop(playerX, playerY, player_change, bulletX, bulletY, bulletX_change, bulletY_change, bullet_state, bulletImg):
    # [...]    

    while running:    
        playerX += player_change

        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                running = False

            # If keystroke is pressed check whether its left or right
            if event.type == pygame.KEYDOWN:
                # [...]               

                if event.key == pygame.K_SPACE:
                    if bullet_state is 'ready':
                        #bullet_sound = mixer.Sound('laser.wav')
                        #bullet_sound.play()
                        # Get the current x coordinate of the spaceship
                        bulletX, bulletY = playerX, playerY
                        bullet_state = 'fire'

Note, the global variable bullet_state

def fire_bullet(x, y):
   global bullet_state
   bullet_state = 'fire'

is different to the local variable bullet_state in game_loop, because bullet_state is an argument to game_loop and thus a completely different variable in a different scope, which has casually the same name:

def game_loop(playerX, playerY, player_change, bulletX, bulletY, 
              bulletX_change, bulletY_change, 
              bullet_state, # <--- that is a new variable in local scope
                            #      and not the "global" bullet_state
              bulletImg):
    # [...]

score 1 · Answer 2 · answered Jan 29 '20 at 21:35

1

        player_change = 0
        playerX += player_change

Try swapping the order of these two lines. Otherwise the change will always be zero when the X location is updated.

answered Jan 29 '20 at 21:35

ballenf

894
10
19

if I swap those them player_change isn't assigned as a variable yet and the playerX += player_change doesnt work – Zach C Jan 30 '20 at 16:29

Pygame Character wont move left or right

2 Answers2