HTTPError: Forbidden when try download image

[snippsat]

They are blocking urllib,but it work with Requests(as you should use anyway).

please write it for me , i cant understand anything

You should try yourself,but to be nice here how to download 1 image.
You always do test like this,before you are making a loop

from bs4 import BeautifulSoup
import requests
import os

page = 4
url = 'https://alpha.wallhaven.cc/random?page={}'.format(page)
url_get = requests.get(url)
soup = BeautifulSoup(url_get.content, 'html.parser')
# Parse
kelimeler = soup.find("img", {"class":"lazyload"})
img_nr = os.path.basename(kelimeler['data-src'])
img_nr = img_nr.split('-')[-1]
img_large = 'https://wallpapers.wallhaven.cc/wallpapers/full/wallhaven-{}'.format(img_nr)
# Download
down_link = requests.get(img_large)
with open(img_nr, "wb") as img_obj:
    img_obj.write(down_link.content)