Hi,

You can link the mako template with python parser file and call the function in mako template like we do in case of rml reports. The difference is in the syntax, which you may understand by referring the following module. Please refer the module and try to understand how the mako template and parser linked. You can see many python function called in that.

https://apps.openerp.com/apps/modules/8.0/account_financial_report_webkit/ 

Also download this file to get an understanding of syntaxes in mako templates:

https://drive.google.com/file/d/0B9fGr6w-dfLWSF9ic3NFeTM5dDQ/edit