Example: HRIS Module

'hr.overtime.application' object

py file:    hr_overtime_application.py
method: approve_all()

Custom module:

my_module.py

class hr_overtime_application(orm.Model):
_inherit = 'hr.overtime.application'

     def approve_all(self, cr, uid, ids, context=None): #same method name
         res = super(hr_overtime_application, self).approve_all(cr, uid, ids, context)
         #add the line

         return res

Hope it will help you :)