Pygame Player Smooth Movement

import pygame
from pygame.sprite import Group, Sprite

class Entity(Sprite):
    # @param anchor is rect position in text form. "topleft", "topright", "center"
    def __init__(self, image, velocity, position, anchor):
        super().__init__()
        self.image = image
        self.rect = image.get_rect()
        setattr(self.rect, anchor, position)
        self.velocity = velocity
        self.position = pygame.Vector2(self.rect.center)

    def move(self, *args):
        if len(args) == 1:
            self.position += args[0]
        else:
            self.position += args

        self.rect.center = self.position

    def set_position(self, *args):
        if len(args) == 1:
            self.position = pygame.Vector2(args[0])
        else:
            self.position = pygame.Vector2(args)

        self.rect.center = self.position

def main():
    pygame.init()
    surface = pygame.display.set_mode((800, 600))
    clock = pygame.time.Clock()
    rect = surface.get_rect()
    running = True
    delta = 0
    fps = 60

    image = pygame.Surface((20, 20), pygame.SRCALPHA)
    image.fill(pygame.Color("firebrick"))

    player = Entity(image, 100, rect.center, "center")
    sprites = Group(player)

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

        direction = pygame.Vector2()
        key_states = pygame.key.get_pressed()
        if any([key_states[k] for k in (pygame.K_UP, pygame.K_w)]):
            direction.y -= 1

        if any([key_states[k] for k in (pygame.K_DOWN, pygame.K_s)]):
            direction.y += 1

        if any([key_states[k] for k in (pygame.K_LEFT, pygame.K_a)]):
            direction.x -= 1

        if any([key_states[k] for k in (pygame.K_RIGHT, pygame.K_d)]):
            direction.x += 1

        if direction != pygame.Vector2():
            # Real world movement.
            direction.normalize_ip()
            player.move(direction * delta * player.velocity)


        surface.fill(pygame.Color("black"))
        sprites.draw(surface)
        pygame.display.flip()
        # Smooth movement
        delta = clock.tick(fps) * 0.001

    pygame.quit()

main()