Which are the most advanced frameworks and tools there are available for python for practicing Behavior Driven Development? Especially finding similar tools as rspec and mocha for ruby would be great.
The Pyccuracy project is an effort to provide a domain-specific language for BDD in Python.  
Unlike doctest, which works at the API level, it encodes higher-level operations such as loading a web page and submitting a form.  I haven't used it but it looks somewhat promising if that is what you're looking for.
Practicing BDD with python