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Besides the extensive predefined libraries, you might want to come up with code on your own to drive your application. This works similarly as in FitNesse. You basically define a static function in your Python code library that reflects the name of the keyword you are using. Instead of camel-casing the function name, you use underscores in Python. Consult the documentation for library authors4 for more in-depth examples on this.
4. http://robotframework.googlecode.com/hg/doc/python/PythonTutorial.html