<p>The log4j network adapter sends events as a serialised java object. I would like to be able to capture this object and deserialise it in a different language (python). Is this possible?</p>

<p><em>NOTE</em> The network capturing is easy; its just a TCP socket and reading in a stream. The difficulty is the deserialising part</p>

Generally, no.
The stream format for Java serialization is defined
in this document
, but you need access to the original class definitions (and a Java runtime to load them into) to turn the stream data back into something approaching the original objects. For example, classes may define writeObject() and readObject() methods to customise their own serialized form.
(
edit:
lubos hasko suggests having a little java program to deserialize the objects in front of Python, but the problem is that for this to work, your "little java program" needs to load the same versions of all the same classes that it might deserialize. Which is tricky if you're receiving log messages from one app, and really tricky if you're multiplexing more than one log stream. Either way, it's not going to be a little program any more.
edit2:
I could be wrong here, I don't know what gets serialized. If it's just log4j classes you should be fine. On the other hand, it's possible to log arbitrary exceptions, and if they get put in the stream as well my point stands.)
It would be much easier to customise the log4j network adapter and replace the raw serialization with some more easily-deserialized form (for example you could use XStream to turn the object into an XML representation)