Filtering planet entries

Here is how to setup liferea not to show me some entries in Planet Debian:

Create a script that reads the rss from stdin, removes the entries you don't want and then writes the rss to stdout;
From the feed properties in liferea, choose the source tab, enable the conversion filter and point that at your script.

Now you just need a simple script that filters the RSS. Here is mine:

#!/usr/bin/python

# Copyright (C) 2007 Enrico Zini <enrico@debian.org>
# This software is licensed under the therms of the GNU General Public
# License, version 2 or later.

import libxml2, re

# What links we should filter out
unwanted = re.compile(r"^(http://feed1.example.com|http://feed2.example.com)")

doc = libxml2.parseFile("-")
root = doc.getRootElement()

# Create an xpath context and register the namespaces
xpc = doc.xpathNewContext()
for d in root.nsDefs():
    if d.name == None:
        xpc.xpathRegisterNs("rss", d.content)
    else:
        xpc.xpathRegisterNs(d.name, d.content)

# Remove unwanted items from the channel list
for x in xpc.xpathEval("/rdf:RDF/rss:channel/rss:items/rdf:Seq/rdf:li"):
    res = x.nsProp("resource", "http://www.w3.org/1999/02/22-rdf-syntax-ns#")
    if unwanted.match(res):
        x.unlinkNode()
        x.freeNode()

# Remove unwanted items from the item list
for x in xpc.xpathEval("/rdf:RDF/rss:item"):
    res = x.nsProp("about", "http://www.w3.org/1999/02/22-rdf-syntax-ns#")
    if unwanted.match(res):
        x.unlinkNode()
        x.freeNode()

# Serialize the result
print doc.saveFormatFile("-", True)

Now, getting to this simple script took some spitting blood. Basically, in Debian we seem to have lots of simple libraries for:

parsing rss, but not outputting it;
outputting rss, but not parsing it;
pasing and outputting rss, but not modifying it.

I tried, in order:

The standard ruby rss module, after seeing this. However, rss.channel.items doesn't seem to be a normal array anymore, and I could not find any documentation on how to modify it.
python-feedparser allows you to read rss and change it, but not to serialize it.
libxml-rss-perl can read, modify and serialize, but serializing loses all the content of the items. Try this script and see:
```
#!/usr/bin/perl -w


use strict;
use warnings;
use XML::RSS;


my $rss = new XML::RSS;
$rss->parsefile("/tmp/rss10.xml");


print $rss->as_string;
```
Update: Nemui Ailin told me that with the most recent upstream version it works. I've reported the bug
libxml-rsslite-perl does not serialize. Plus, it parses rss via crude regexps and its manpage has a longish list of things that can go wrong.
libmrss0-dev has only a README that points to example files that are not packaged. I reported it as a bug.
The description of any other module that I could find that would mention rss was quite clearly showing that it didn't support one of the three (read, edit, reserialize) features that I needed. With a quick look at the code, I couldn't find out if cl-rss supported serialisation.