I’m trying to make a square character sprite in pygame. Can you please look at my code and tell me what I did wrong? Link to video about it - pygame

Question

a youtube video told me to put what I've already put.
https://www.youtube.com/watch?v=bVx2nhB0t1o&feature=youtu.be
My window opens, but just stays at a black screen. When I close the window, then I get the error message:
Traceback (most recent call last):
File "./invaders.py", line 23, in <module>
keys = pygame.key.get_pressed()
pygame.error: video system not initialized
I don't really understand why this is happening and any help would be much appreciated.
import pygame
pygame.init()
win = pygame.display.set_mode((500, 500))
pygame.display.set_caption("Space Invaders")
x = 50
y = 50
width = 30
height = 30
vel = 5
run = True
while run:
pygame.time.delay(100)
for event in pygame.event.get():
if event.type == pygame.QUIT:
run = False
pygame.quit()
keys = pygame.key.get_pressed()
if keys[pygame.K_LEFT]:
x -= vel
if keys[pygame.K_RIGHT]:
x += vel
if keys[pygame.K_UP]:
y -= vel
if keys[pygame.K_DOWN]:
y += vel
win.fill(0)
pygame.draw.rect(win, (255, 0, 0), (x, y, width, height))
pygame.display.update()

Answer 1

Your code is mixed-up. Generally PyGame applications have a "main loop" which handles the event loop, processes any user input, and then re-draws the screen.
Your code has all of these elements, but a whole block of code is not inside the main loop, it's only executed after the window has been closed. You need to be careful of the placement and indentation.
This code below is basically your exact code, re-arranged with some tweaks.
import pygame
BLACK = ( 0, 0, 0 ) # colours
RED = (255, 0, 0 )
pygame.init()
win = pygame.display.set_mode((500, 500))
pygame.display.set_caption("Space Invaders")
x = 50
y = 50
width = 30
height = 30
vel = 5
clock = pygame.time.Clock()
run = True
# Main loop
while run:
#pygame.time.delay(100) # <-- don't use delays like this
# handle the PyGame event loop
for event in pygame.event.get():
if event.type == pygame.QUIT:
run = False
# handle user movement
keys = pygame.key.get_pressed()
if keys[pygame.K_LEFT]:
x -= vel
if keys[pygame.K_RIGHT]:
x += vel
if keys[pygame.K_UP]:
y -= vel
if keys[pygame.K_DOWN]:
y += vel
# repaint the window
win.fill( BLACK )
pygame.draw.rect( win, RED, ( x, y, width, height ) )
pygame.display.update()
clock.tick( 10 ) # limit the FPS here
# main loop has ended, quit
pygame.quit()
Now the window painting, and user-input handling is now moved inside the scope of the main loop.
Also it's best not to add fixed time delays into PyGame code. Adjust the frame rate using a PyGame clock.