The previous example wasn’t very useful other than as a tool to explain how threads work. So in this example, we will create a Thread class that can download files from the internet. The U.S. Internal Revenue Service has lots of PDF forms that it has its citizens use for taxes. We will use this free resource for our demo. Here’s the code:

Python

# Python 2 version
import os
import urllib2
from threading import Thread
class DownloadThread(Thread):
    """
    A threading example that can download a file
    """
    def __init__(self, url, name):
        """Initialize the thread"""
        Thread.__init__(self)
        self.name = name
        self.url = url
    def run(self):
        """Run the thread"""
        handle = urllib2.urlopen(self.url)
        fname = os.path.basename(self.url)
        with open(fname, "wb") as f_handler:
            while True:
                chunk = handle.read(1024)
                if not chunk:
                    break
                f_handler.write(chunk)
        msg = "%s has finished downloading %s!" % (self.name,
                                                   self.url)
        print(msg)
def main(urls):
    """
    Run the program
    """
    for item, url in enumerate(urls):
        name = "Thread %s" % (item+1)
        thread = DownloadThread(url, name)
        thread.start()
if __name__ == "__main__":
    urls = ["http://www.irs.gov/pub/irs-pdf/f1040.pdf",
            "http://www.irs.gov/pub/irs-pdf/f1040a.pdf",
            "http://www.irs.gov/pub/irs-pdf/f1040ez.pdf",
            "http://www.irs.gov/pub/irs-pdf/f1040es.pdf",
            "http://www.irs.gov/pub/irs-pdf/f1040sb.pdf"]
    main(urls)

Writing a Threaded Downloader