I am looking for an open source monitoring solution (preferably in Python) that works with ssh or snmp and does not require the installation of an agent (like Nagios, ZenOSS, munin). 
Are you aware of such a solution?
All tools that allow you to run scripts to gather metrics can basically run commands over a ssh connection on the target box. 
The question is though if this makes a lot of sense as you rely on the network connection always being available and for each (set of) property(s) you need to run a new remote connection with all its overhead.
Snmp does by definition of the protocol require you to run an snmp agent on the target box.
open source monitoring solution without the need of an agent