Beginning Space Invaders Code and Requiring Assistance with a part of it

I am beginning to code a space invaders game and trying to just get the ship down and let it move back and forth across the screen. I'm very beginner status so it is a big challenge for me. Whenever I try to run it it tells me that I'm requiring another positional argument in my update function but I don't understand what I'm supposed to do.

I've tried moving around the variable initialization for keys but it hasn't changed anything. If anyone wants to take a look at my code and tell me what I could do it would be amazing.

import pygame, sys
from pygame import *
pygame.init()
screen = pygame.display.set_mode((800,600))
pygame.display.set_caption("Space Invaders")
pygame.mouse.set_visible(0)
WIDTH = 800
vel = 5
width = 64
keys = pygame.key.get_pressed()
BLACK = (0, 0, 0)

all_sprites = pygame.sprite.Group()
class Player(pygame.sprite.Sprite):
    def _init_(self):
        pygame.sprite.Sprite._init_(self)
        self.image = pygame.image.load("images\ship.png")
        self.rect = self.image.get_rect()
        self.rect.center = (WIDTH/2, 40)
    def update(self, keys, *args):
        if keys[pygame.K_LEFT] and self.rect.x > vel:
            self.rect.x -= vel
        if keys[pygame.K_RIGHT] and self.rect.x < 800 - width - vel:
            self.rect.x += vel 
        screen.blit(self.image, self.rect)

player = Player()
all_sprites.add(player)

run = True
while run:
    pygame.time.delay(100)
    pygame.display.update()
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
    all_sprites.update()

    screen.fill(BLACK)
    all_sprites.draw(screen)

    pygame.display


pygame.quit()

I know this is just the beginning but I can't figure out what I'm missing here.

Solution

You've to pass the current states of the keyboard buttons to .update(). Note, the arguments which are passed to all_sprites.update() are delegated to player.update(). all_sprites is pygame.sprite.Group object. The .update() method calls .update() on each contained sprite and pass the parameters through.

Get the states of the keyboard buttons by pygame.key.get_pressed() and pass it to .update:

keys = pygame.key.get_pressed()
all_sprites.update(keys)

The name of the constructor has to be __init__ rather than _init_ . See Class:

class Player(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        # [...]