Python complex event processing
Casual browsing indicates that this is not a very common problem domain for Python (although very interesting!). The framework that closest come to my mind is PEAK-Rules or dynrules.
There might be more, but not widely known (I'll search a bit more)
For your own digging: the place to find Python projects is first and foremost PyPI.
(@cues7a: Twisted, while indeed being an event framework, is too low-level to be comparable to Esper.)
Edit: It seems you can control Sybase's CEP products with Python
The ruleCore CEP Server uses dynamically loaded Python modules which can be used to extend it. The internal architecture is build around a central event bus which uses a pub/sub approach. So each module can subscribe to internal events and publish events based on logic inside the module.