Pygame displays a black screen

I did some research to see if I could fix my problem on my own but it has been fruitless so far. I’ve checked to see if I ran the .display command too much but I haven’t, the program will run without error but the screen appears black except when I close the window out, you can catch a glimpse of what it is supposed to display. Any insight into what is wrong? Help is greatly appreciated!

import math
import random

import pygame
from pygame import mixer

# Initialize the pygame
pygame.init()

# create the screen
screen = pygame.display.set_mode((800, 600))

# Background
background = pygame.image.load('space background.png')

# Background Sound
# come back to this from bg music   'mixer.music.load('insert file name')'
# 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('ship.png')
playerX = 370
playerY = 480
playerX_change = 0

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

for i in range(num_of_enemies):
    enemyImg.append(pygame.image.load('enemy.png'))
    enemyX.append(random.randint(0, 735))
    enemyY.append(random.randint(50, 150))
    enemyX_change.append(0.3)
    enemyY_change.append(40)

# Bullet

# Ready -  you cat see the bullet on the screen
# Fire - The bullet is currently moving

bulletImg = pygame.image.load('bullet.png')
bulletX = 0
bulletY = 480
bulletX_change = 0
bulletY_change = 1  # Bullet speed
bullet_state = "ready"

# Score

score_value = 0
font = pygame.font.Font('Minecraft.ttf', 24)
textX = 10
testY = 10  # might have to change back to 'text'

# Game Over text
over_font = pygame.font.Font('Minecraft.ttf', 64)


def show_score(x, y):
    score = font.render("Score : " + str(score_value), True, (225, 225, 255))
    screen.blit(score, (x, y))


def game_over_text(x, y):
    over_text = over_font.render("GAME OVER", True, (225, 225, 255))
    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


# Game Loop
running = True
while running:

    # RGB
    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 right or left
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                playerX_change = -0.7  # player speed
            if event.key == pygame.K_RIGHT:
                playerX_change = 0.7
            if event.key == pygame.K_SPACE:
                if bullet_state == "ready":
                    bullet_Sound = mixer.Sound('laser.wav')
                    bullet_Sound.play()
                    # Get the current X corrdinate of te spaceship
                    bulletX = playerX
                    fire_bullet(playerX, bulletY)

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

    # 5 = 5 + -0.1 -> 5 = 5 - 0.1
    # 5 = 5 + 0.1

    # Checking for boundries of spaceship
    playerX += playerX_change
    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] = 0.3  # enemy speed
            enemyY[i] += enemyY_change[i]
        elif enemyX[i] >= 736:
            enemyX_change[i] = -0.3
            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 += 100
            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 == "fire":
    fire_bullet(bulletX, bulletY)
    bulletY -= bulletY_change

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

Answer

All you have to do is indent the last bit of code (the 11 lines under the comment Bullet Movement) one level in. Right now, it’s not under the while loop, which explains why the screen is black and why it only appears after you click the close button (which exits the loop and executes the drawing code). Hope this helps!