How to use the ta.models.TACourse.objects.filter function in ta

def view_contract(request, post_slug, userid):
    #contract = get_object_or_404(TAContract, pk=contract_id)
    #ta courses get all courses with contract_id
    #courses = TACourse.objects.filter(contract=contract)
    #contract.pay_per_bu = format_currency(contract.pay_per_bu)
    #contract.scholarship_per_bu = format_currency(contract.scholarship_per_bu)
    
    posting = get_object_or_404(TAPosting, slug=post_slug, unit__in=request.units)
    if posting.unit not in request.units:
        ForbiddenResponse(request, 'You cannot access this page')
    contract = get_object_or_404(TAContract, posting=posting, application__person__userid=userid)
    courses = TACourse.objects.filter(contract=contract)
    
    total = contract.total_bu()
    bu = contract.bu()
    
    pp = posting.payperiods()
    salary_sem = (total*contract.pay_per_bu)
    schol_sem = (bu*contract.scholarship_per_bu)
    salary_sem_out = _format_currency(salary_sem)
    schol_sem_out = _format_currency(schol_sem)
    salary_bi = _format_currency(salary_sem / pp)
    schol_bi = _format_currency(schol_sem / pp)


    context =   {'posting': posting,
                 'contract':contract,
                 'courses':courses,

def total_pay(self, offering):
        """
        Payments for all tacourses associated with this offering 
        """
        total = 0
        tacourses = TACourse.objects.filter(course=offering, contract__posting=self).exclude(contract__status__in=['REJ', 'CAN'])
        for course in tacourses:
            total += course.pay()
        return total