HTTPError: Forbidden when try download image

[b33g33]

i want to download picture on wallhaven.cc and i can get picture url but image is not download its give an error ; 

my code is ;

import urllib.request
from bs4 import BeautifulSoup

imdbUrl="htt"+"ps:"+"//alpha.wallhaven.cc"+"/random?page=4"
r=requests.get(imdbUrl)

soup=BeautifulSoup(r.content,"html.parser")

kelimeler=soup.find_all("img",{"class":"lazyload"})

say=0
for i in kelimeler:
    say +=1
    url=str(i['data-src'])
    url=url.replace("alpha","wallpapers")
    url=url.replace("/thumb/small/th-","/full/wallhaven-")
    url=url.replace("https","http")
    yeniad=str(say)+".jpg"
    url=url.strip()
    print(url)
    urllib.request.urlretrieve(url,yeniad)

but its give an error like this ; 

Error:
HTTPError: Forbidden