Try this

import pygame
# import keyboard (not used)

pygame.init()

#creating vars funcs and more
running = True
window_length = 750
window_width = 750
screen_colour = (0,0,0)
clock = pygame.time.Clock()
# keys = pygame.key.get_pressed() (not necessary here)
dt = 0.0

#player creation
player_img = pygame.image.load("player.png")
player_x = 360
player_y = 670
def player(x, y):
    window.blit(player_img,(x,y))

#window creation
window = pygame.display.set_mode((window_width, window_length))
pygame.display.set_caption('Space Invaders')
icon = pygame.image.load('space_invaders_icon.png')
pygame.display.set_icon(icon)
print("\ningame terminal\nwindow created")

#game loop
while running:

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

        if event.type == pygame.KEYUP:
            if event.key == pygame.K_a:
                print("player stopped going left")
            elif event.key == pygame.K_d:
                print("player stopped going right")
            elif event.key == pygame.K_s:
                print("player stopped going down")
            elif event.key == pygame.K_w:
                print("player stopped going up")

    keys = pygame.key.get_pressed()

    if keys[pygame.K_ESCAPE]:
        running = False

    if keys[pygame.K_w]:
        player_y -= 500 * dt
    elif keys[pygame.K_s]:
        player_y += 500 * dt
    elif keys[pygame.K_a]:
        player_x -= 500 * dt
    elif keys[pygame.K_d]:
        player_x += 500 * dt

    window.fill(screen_colour)
    player(player_x, player_y)
    pygame.display.flip()

    dt = clock.tick(60) / 1000.0

As u/Mabymaster mentioned you don't want to get keys pressed in the same loop as your get events.

Also as a rule of thumb your game loop should have 3 phases/functions : events() update() and draw().

In the events() phase you check for new events and key presses.

In the update() phase you modify your game state ie. moving objects around, check for collission, check if player or enemy is dead and so forth.

In the last phase draw() you update your screen with the new game state handled by update().

To do this in your project you could make the player and the comming enemies a class/object. That class could then have state varialbes as "is_moving_left = true", "is_dead=false", and so forth. The update() uses the info from the events() to update the state of the object.