from urllib.request import urlretrieve
import requests
from multiprocessing import Pool

def download(i):
    try:
        headers = requests.head("http://www.site.com/scripts/getfile.php?id={}".format(i))
    except:
        print("Unable to reach file " + str(i))
        return None
    try:
        filename = headers.headers["content-disposition"].replace("filename=", "")
        filename = "{}_{}".format(i, filename)
    except:
        filename = str(i)
    urlretrieve("http://www.site.com/scripts/getfile.php?id={}".format(i), "/Volumes/SeagateExpansion/Database/{}".format(filename))
    print("Downloaded {}".format(filename))

p = Pool(processes = 16)
p.map(download, range(70000))
p.close()
p.join()


ERROR:
Traceback (most recent call last):
  File "/Users/MyUsername/Dropbox/Python/Projects/FileDownloader.py", line 20, in <module>
    p.map(download, range(70000))
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/pool.py", line 260, in map
    return self._map_async(func, iterable, mapstar, chunksize).get()
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/pool.py", line 599, in get
    raise self._value
multiprocessing.pool.MaybeEncodingError: Error sending result: '<multiprocessing.pool.ExceptionWithTraceback object at 0x1027a67f0>'. Reason: 'TypeError("cannot serialize '_io.BufferedReader' object",)'