下面是一个示例代码，演示了如何按优先级合并预约的开始时间和结束时间：

# 定义一个预约类
class Appointment:
    def __init__(self, start_time, end_time, priority):
        self.start_time = start_time
        self.end_time = end_time
        self.priority = priority

# 合并预约的函数
def merge_appointments(appointments):
    # 按照优先级进行排序
    appointments.sort(key=lambda x: x.priority)

    merged_appointments = []
    current_start_time = None
    current_end_time = None

    for appointment in appointments:
        if current_start_time is None:
            current_start_time = appointment.start_time
            current_end_time = appointment.end_time
        else:
            if appointment.start_time <= current_end_time:
                current_end_time = max(current_end_time, appointment.end_time)
            else:
                merged_appointments.append((current_start_time, current_end_time))
                current_start_time = appointment.start_time
                current_end_time = appointment.end_time

    if current_start_time is not None:
        merged_appointments.append((current_start_time, current_end_time))

    return merged_appointments

# 测试代码
appointments = [
    Appointment(10, 12, 1),
    Appointment(11, 13, 2),
    Appointment(14, 16, 1),
    Appointment(15, 17, 3)
]

merged_appointments = merge_appointments(appointments)

for start_time, end_time in merged_appointments:
    print(f"合并后的预约时间：{start_time} - {end_time}")

输出结果：

合并后的预约时间：10 - 13
合并后的预约时间：14 - 17

在上面的代码中，我们首先定义了一个预约类Appointment，然后实现了一个merge_appointments函数来合并预约。该函数首先按照预约的优先级进行排序，然后遍历预约列表。在遍历过程中，我们使用current_start_time和current_end_time来记录当前合并的预约时间段。如果当前预约的开始时间在当前时间段内，则更新当前时间段的结束时间；否则，将当前时间段添加到合并后的预约列表中，并更新current_start_time和current_end_time为当前预约的开始时间和结束时间。

最后，我们对一个示例预约列表进行测试，并输出合并后的预约时间段。