Core Python Programming (2nd Edition)

deltas = [ x[1]-x[0] for x in partition() ]
print deltas
print sum(deltas)
[0.10271966686994982, 0.13826576491042208, 0.064146913555132801,
0.11906452454467387, 0.10501198456091299, 0.011732423830768779,
0.11785369256442912, 0.065927165520102249, 0.098351305878176198,
0.077786747076205365, 0.099139810689226726]
1.0
Of course, the output will always be different since articles are always being posted. No two executions
will result in the same output unless your news server has not been updated with another article since
you last ran the script.
Line-by-Line Explanation
Lines 19
This application starts with a few import statements and some constants, much like the FTP client
example.
Lines 1140
In the first section, we attempt to connect to the NNTP host server and bail if it tails (lines 13-24). Line
15 is commented out deliberately in case your server requires authentication (with login and password)if
so, uncomment this line and edit it in with line 14. This is followed by trying to load up the specific
newsgroup. Again, it will quit if that newsgroup does not exist, is not archived by this server, or if
authentication is required (lines 26-40).
Lines 4255
In the next part we get some headers to display (lines 42-51). The ones that have the most meaning
are the author, subject, and date. This data is retrieved and displayed to the user. Each call to the xhdr
() method requires us to give the range of articles to extract the headers from. We are only interested
in a single message, so the range is "X-X" where X is the last message number.
xhdr() returns a 2-tuple consisting of a server response (rsp) and a list of the headers in the range we
specify. Since we are only requesting this information for one message (the last one), we just take the
first element of the list (hdr [0]). That data item is a 2-tuple consisting of the article number and the
data string. Since we already know the article number (because we give it in our range request), we are
only interested in the second item, the data string (hdr [0][1] ).
The last part is to download the body of the article itself (lines 53-55). It consists of a call to the body()
method, a display the first 20 or fewer meaningful lines (as defined at the beginning of this section), a
logout of the server, and complete execution.
Lines 5780
The core piece of processing is done by the displayFirst20() function (lines 57-80). It takes the set of