from collections import defaultdict

def per_manager(timesheets):
    per_manager = defaultdict(list)
    # filter timesheets per manager
    for timesheet in [t for t in timesheets if need_manager_mail(t)]:
        manager_id = timesheet.approver
        per_manager[manager_id].append(timesheet)
    return per_manager

def need_manager_mail(timesheet):
    return not timesheet.is_submitted() or not timesheet.is_approved()

def employees(timesheets):
    return dict([(t.employee.id, t.employee) for t in timesheets])