downloader.py

import requests
import re
from multiprocessing import Pool

url = "http://www.cs.umd.edu/~gasarch/bookrev/bookrev.html"
r_url = re.compile("HREF=.*.pdf\"")
r_replace_t = "HREF=\""
r_replace_w = "http://www.cs.umd.edu/~gasarch/bookrev/"

site_content = requests.get(url).content
links = [s.replace(r_replace_t, r_replace_w).replace("\"", "")
         for s in r_url.findall(site_content)]

def saver(link):
    with open(link.split("/")[-1], "wb") as ff:
        ff.write(requests.get(link).content)

pool = Pool(8)
pool.map(saver, links)
pool.close()
pool.join()