Hi just try this on python code section under salary rule definition 

if contract.employee_id.gender = "Male":
result = your logic
else contract.employee_id.gender = "Female"
result = your logic

I tried using delegation inheritance and also inheriting models directly. When i am using two models in a list using like _inherit = ['hr.payroll' , 'hr.contract'] , the error is that the class does not exist. and _inherit ='hr.payroll' _inherits = {'hr.contract' : 'wage'} , the error is ALTER TABLE "hr_salary_rule" ALTER COLUMN "wage" SET NOT NULL'