My python code has stopped detecting keystrokes

Question

It was working before, then I added the enemy rectangle and it has stopped working.

import time, copy
import pygame
import random
import os
WINDOW_WIDTH = 560
WINDOW_HEIGHT = 560
WINDOW = pygame.display.set_mode((WINDOW_WIDTH, WINDOW_HEIGHT))
red =(255,0,0)
green =(0,255,50)
yellow =(255,255,0)
black = (0,0,0)
white = (255,255,255)
WINDOW.fill(black)
pygame.display.update()
a = 20
b = 20
L = False
R = False
U = False
D = False
##x = [20,40,60,80,100,120,140,160,180,200,220,240,260,280,300,320,340,360,380,400,420,440,460,480,500,520]
##ex = x[random.randint(0,24)]
##ey = x[random.randint(0,24)]
player = pygame.Rect(a,b,20,20)
pygame.draw.rect(WINDOW, green, player)
##enemy = pygame.Rect(ex,ey,20,20)
##pygame.draw.rect(WINDOW, red, enemy)
pygame.display.update()
while True:
    for event in pygame.event.get():
        if event.type == pygame.KEYDOWN:                  
            if event.key == pygame.K_LEFT:        
                L = True
            elif event.key == pygame.K_RIGHT:    
                R = True
            elif event.key == pygame.K_UP:       
                U = True
            elif event.key == pygame.K_DOWN:    
                D = True
        elif event.type == pygame.KEYUP:
            if event.key == pygame.K_LEFT:
                L = False
            elif event.key == pygame.K_RIGHT:     
                R = False
            elif event.key == pygame.K_UP:       
                U = False
            elif event.key == pygame.K_DOWN:     
                D = False
        if(D):
            if b < 540:
                pygame.draw.rect(WINDOW, black, player)
                b = b+20
                player = pygame.Rect(a,b,20,20)
                pygame.draw.rect(WINDOW, green, player)
        elif(U):
            if b != 0:
                pygame.draw.rect(WINDOW, black, player)
                b = b-20
                player = pygame.Rect(a,b,20,20)
                pygame.draw.rect(WINDOW, green, player)
        elif(R):
            if a < 540:
                pygame.draw.rect(WINDOW, black, player)
                a = a+20
                player = pygame.Rect(a,b,20,20)
                pygame.draw.rect(WINDOW, green, player)
        elif(L):
            if a != 0:
                pygame.draw.rect(WINDOW, black, player)
                a = a-20
                player = pygame.Rect(a,b,20,20)
                pygame.draw.rect(WINDOW, green, player)
##        time.sleep(0.2)
##        if ex < a:
##            pygame.draw.rect(WINDOW, black, enemy)
##            ex = ex+20
##            enemy = pygame.Rect(ex,ey,20,20)
##            pygame.draw.rect(WINDOW, red, enemy)
##        elif ex > a:
##            pygame.draw.rect(WINDOW, black, enemy)
##            ex = ex-20
##            enemy = pygame.Rect(ex,ey,20,20)
##            pygame.draw.rect(WINDOW, red, enemy)
##        elif ey > b:
##            pygame.draw.rect(WINDOW, black, enemy)
##            ey = ey-20
##            enemy = pygame.Rect(ex,ey,20,20)
##            pygame.draw.rect(WINDOW, red, enemy)
##        elif ey > b:
##            pygame.draw.rect(WINDOW, black, enemy)
##            ey = ey-20
##            enemy = pygame.Rect(ex,ey,20,20)
##            pygame.draw.rect(WINDOW, red, enemy)
##        pygame.display.update()
##        if ex == a and ey == b:
##            WINDOW.fill(white)
##            pygame.display.update()
##            time.sleep(2)
##            os._exit(1)

Answer 1

I've never used Pygame, but I'm pretty sure you're supposed to be updating the display in the main loop, not outside.

pygame.display.update() on line 28 should be inside the loop, so under the while True: part.

I noticed that you had an update further down, but you commented it out.