Why does using pygame.Event.key throw an error only when outside of an "if event.type == pygame.locals.KEYDOWN" block?

I've been making a game using PyGame/Python, and recently I've run into something strange: I'm unable to use pygame.Event.key outside of an if event.type == pygame.locals.KEYDOWN block.

Here's the relevant section of the code. This throws no errors and reacts to events as expected:

import pygame
import pygame.locals
import sys
import time

WINDOW = pygame.display.set_mode((500,500))

pygame.init()
pygame.display.set_caption("The Game of Awesomeness")

def update_screen():
    #Code to update screen
    pass

while True:
    for event in pygame.event.get():
        if event.type == pygame.locals.KEYDOWN:
            if event.key == pygame.locals.K_q:
                pygame.quit()
                sys.exit()

            elif event.key == pygame.locals.K_w:
                pass
            elif event.key == pygame.locals.K_d:
                pass
            elif event.key == pygame.locals.K_s:
                pass
            elif event.key == pygame.locals.K_a:
                pass

    update_screen()
    time.sleep(0.1)

But if I simply comment out the line if event.type == pygame.locals.KEYDOWN, it doesn't work:

import pygame
import pygame.locals
import sys
import time

WINDOW = pygame.display.set_mode((500,500))

pygame.init()
pygame.display.set_caption("The Game of Awesomeness")

def update_screen():
    #Code to update screen
    pass

while True:
    for event in pygame.event.get():
        #if event.type == pygame.locals.KEYDOWN:
            if event.key == pygame.locals.K_q:
                pygame.quit()
                sys.exit()

            elif event.key == pygame.locals.K_w:
                pass
            elif event.key == pygame.locals.K_d:
                pass
            elif event.key == pygame.locals.K_s:
                pass
            elif event.key == pygame.locals.K_a:
                pass

    update_screen()
    time.sleep(0.1)

With the if statement commented out I get the following error the first time any event occurs:

Traceback (most recent call last):
  File "C:/Users/Username/Desktop/program.py", line 18, in <module>
    if event.key == pygame.locals.K_q:
AttributeError: 'Event' object has no attribute 'key'

The only difference between the two programs is that the first one has the statement if event.type == pygame.locals.KEYDOWN, and the second one does not. Note that the code within the if statement in the working program does run when it should, meaning the if event.key == pygame.locals.K_keyname statements all run without throwing errors. Based on the error it seems that pygame.Event.key can only be referenced within an if event.type == pygame.locals.KEYDOWN block.

Why is pygame.Event.key behaving this way?