add 2 & 3 compatibility

Author: clouds56

download.py

@@ -1,18 +1,21 @@
+from __future__ import print_function
 import os
 import re
-import urllib2
+from six.moves.urllib.request import urlopen
+from six.moves.urllib.error import HTTPError
 import shutil
 import argparse
 import mistune
 import bs4 as BeautifulSoup
+import socket
 
 def download_pdf(link, location, name):
     try:
-        response = urllib2.urlopen(link, timeout=500)
+        response = urlopen(link, timeout=500)
         file = open(os.path.join(location, name), 'w')
         file.write(response.read())
         file.close()
-    except urllib2.HTTPError:
+    except HTTPError:
         print('>>> Error 404: cannot be downloaded!\n') 
         raise   
     except socket.timeout:

requirements.txt

@@ -1,2 +1,3 @@
 mistune>=0.7.2
-beautifulsoup4>=4.4.1
+beautifulsoup4>=4.4.1
+six>=1.10.0