Now, we are going to write our Python script using the urllib module. For this, create a text file called RFC_download_urllib.py:

#!/usr/bin/env python3

import sys, urllib.request
try:
    rfc_number = int(sys.argv[1])
except (IndexError, ValueError):
    print('Must supply an RFC number as first argument')
    sys.exit(2)
template = 'http://www.rfc-editor.org/rfc/rfc{}.txt'
url = template.format(rfc_number)
rfc_raw = urllib.request.urlopen(url).read()
rfc = rfc_raw.decode()
print(rfc)

We can run the preceding code by using the following command:

$ python RFC_download_urllib.py 2324

This is the output of the previous script, where we can see the RFC description document:

First, we import our modules and check whether an RFC number has been supplied on the command line. Then, we construct our URL by substituting the supplied RFC number. Next, the main activity, the urlopen() call, will construct an HTTP request for our URL, and then it will connect to the IETF web server and download the RFC text. Next, we decode the text to Unicode, and finally we print it out to the screen.