Question

When i try to run this simple game. it says:

    screen.blit(plumbers,(50 + M ,337 + N))
UnboundLocalError: local variable 'M' referenced before assignment

this is from the bellow code:

import pygame
import os, sys
import itertools
import pygame
from pygame.sprite import Sprite

cloud_background = pygame.image.load('clouds.bmp')
brick_tile = pygame.image.load('brick_tile.png')
plumbers = pygame.image.load('Mario_sideways_sprite_2xL.png')

pink = (255, 64, 64)
w = 640
h = 480
screen = pygame.display.set_mode((w, h))
running = 1

def setup_background():
    screen.fill((pink))
    screen.blit(cloud_background,(0,0))
    brick_width, brick_height = brick_tile.get_width(), brick_tile.get_height()
    for x,y in itertools.product(range(0,640,brick_width),
                                 range(390,480,brick_height)):
        # print(x,y)
        screen.blit(brick_tile, (x,y))


def show_sprites():
    screen.blit(plumbers,(50 + M ,337 + N))
    if event.key == pygame.K_UP:
        M = 1
        N = 0

while running:
    setup_background()
    show_sprites()
    move()
    event = pygame.event.poll()
    if event.type == pygame.QUIT: sys.exit()

But when i add the variable above “screen.blit” so it looks like this:

def show_sprites():
    if event.key == pygame.K_UP:
        M = 1
        N = 0
    screen.blit(plumbers,(50 + M ,337 + N))

I get this error:

Traceback (most recent call last):
  File "C:\Users\Enrique\Dropbox\GAMEZ_PYGAME\gamez.py", line 36, in <module>
    show_sprites()
  File "C:\Users\Enrique\Dropbox\GAMEZ_PYGAME\gamez.py", line 28, in show_sprites
    if event.key == pygame.K_UP:
NameError: global name 'event' is not defined

What do i have to add/ change to get these simple controls to work?

Answer 1

That means you have two problems. Python sees the first one and stops with an exception.

In :

def show_sprites():
    screen.blit(plumbers,(50 + M ,337 + N))
    .......

M and N still don’t exist when called.
Try for example:

def show_sprites():
    print M, N
    screen.blit(plumbers,(50 + M ,337 + N))
    .......

In

def show_sprites():
    if event.key == pygame.K_UP:

neither event has been defined.

You should check a tutorial about function arguments/parameters and local variables.

your function should looks like this (for example):

def show_sprites(M, N, event):

or most likely:

def show_sprites(event):
    if event.key == pygame.K_UP:
        M = 1
        N = 0
    else:
        M = 0  # ? up to you
        N = 0  # ?
    screen.blit(plumbers,(50 + M ,337 + N))

with:

while running:
    setup_background()
    event = pygame.event.poll()
    if event.type == pygame.QUIT: sys.exit()
    show_sprites(event)
    move()

Finally, this code will send all kind of events to your function so you should filter them:

if event.type == pygame.QUIT:
    sys.exit()
elif event.type == pygame.KEYDOWN:
    show_sprites(event)
    move()

check this for example