[galaxy-dev] referring to tool_data_tables[] structure

I've seen $__app__.tool_data_tables[ 'all_fasta' ].get_fields() )[0][-1] in tool xml templates. Is there a way I can access the tool_data_tables structure from python code too? I see all the initialization stuff happening in https://bitbucket.org/abrenner/galaxy-central/src/f3e736fe03df3a6dd5438c12ba... But not seeing where one can access any of these app variables? Regards, Damion