Writing an HTTP fail-over client with resume and partial downloading

You would like to create a fail-over client that will resume downloading a file if it fails for any reason in the first instance.

How to do it...

Let us download the Python 2.7 code from http://www.python.org. A resume_download() file will resume any unfinished download of that file.

Listing 4.9 explains resume downloading as follows:

#!/usr/bin/env python 
# Python Network Programming Cookbook -- Chapter - 4 
# This program requires Python 3.5.2 or any later version 
# It may run on any other version with/without modifications. 
# 
# Follow the comments inline to make it run on Python 2.7.x. 
 
import urllib.request, urllib.parse, urllib.error 
# Comment out the above line and uncomment the below for Python 2.7.x. 
#import urllib 
 
import os 
 
TARGET_URL = 'http://python.org/ftp/python/2.7.4/' 
TARGET_FILE = 'Python-2.7.4.tgz' 
 
class CustomURLOpener(urllib.request.FancyURLopener): 
# Comment out the above line and uncomment...