PyGame paddle board not moving

Question

The key events are being registered fine on the console. Also, my paddle is showing up which suggests that my paddle class called from another file works. However, I would like my paddle to move smoothly when the left arrow key or the right arrow key is pressed down so the user does not have to repeatedly click. However, with my current code, the paddle does not move at all. I've tried changing around the position of the if/else statement that changes position to no avail. What am I doing wrong here?

The main game:

import pygame
from pygame.locals import *

from Config import Config 
from Paddle import Paddle

pygame.init()

#--Display settings
pygame.display.set_caption(Config['game']['caption'])
game_display = pygame.display.set_mode((Config['game']['display_width'], 
Config['game']['display_height']))
clock = pygame.time.Clock()
paddle= Paddle(game_display)

x_change = 0
pressed_left = False
pressed_right = False

def event_handler():
for event in pygame.event.get():
    print (event)
    if (event.type == QUIT) or (event.type == KEYDOWN and event.key == 
K_ESCAPE):
        pygame.quit()
        quit()

    #To move the paddle to the left and right
    if event.type == KEYDOWN:
        if event.key == K_LEFT:
            pressed_left = True  
        elif event.key== K_RIGHT:
            pressed_right = True

    #If the key is up
    if event.type == KEYUP:
        if event.key == K_LEFT:
            pressed_left = False
            x_change = 0
        elif event.key == K_RIGHT:
            pressed_right = False 
            x_change = 0

#--This changes the position
if pressed_left:
    x_change = -5
if pressed_right:
    x_change = 5

while True:
    event_handler()
    game_display.fill(Config['colors']['white'])
    paddle.draw()
    paddle.movement(x_change)

    pygame.display.update()
    clock.tick(Config['game']['fps'])

And from my paddle.py that contains the Paddle class:

import pygame
from pygame.locals import *

from Config import Config

class Paddle:
    def __init__(self, game_display):
        self.x = (Config['game']['display_width'] * 0.45)
        self.y = (Config['game']['display_height'] * 0.92)
        self.game_display=game_display


    def draw(self):
        pygame.draw.rect(self.game_display, Config['colors']['red'], 
[self.x, self.y, 40, 25])

    def movement(self, x_change):
        self.x += x_change

user_2676937 · Answer

Let's look at a simpler example. Try running this program.

pressed_left = False
def event_handler():
    pressed_left = True

event_handler()

print(pressed_left)

While you expected the program to print True, it prints False. This happens due to the way variable scoping works in python. When you try to modify a variable in a function that isn't defined in that function itself, python defines a new variable instead of looking for a global one. So, the pressed_left = True line in event_handler() just creates a new pressed_left variable that exists solely in the event_handler function without modifying the global one.

To solve this, you need to declare the variable as global in the function. Try running this program.

pressed_left = False
def event_handler():
    global pressed_left
    pressed_left = True

event_handler()

print(pressed_left)

user_10584721 · Answer

change your keys to something like this

key = pygame.key.pressed()

if key[pygame.K_left]:
    pygame movement

PyGame paddle board not moving

2 Answers