如何获取复杂数组中列表的第二小值？公交API场景问题处理

问题背景 #

我用以下代码从API获取指定线路最早公交出发时间的剩余分钟数：

soonestDepartureTimeUnix = min(item["departure_time"] for item in tsl105513Route2["itineraries"][0]["schedule_items"])
minutes = int((soonestDepartureTimeUnix - (time.time()))/60)

但当minutes为0时，这个结果对路人没有实际意义，需要获取第二早的出发时间来替代。

API响应结构 #

{
    "route_departures": [
        {
            "global_route_id": "TSL:105513",
            "itineraries": [
                {
                    "branch_code": "",
                    "direction_headsign": "*******",
                    "direction_id": 1,
                    "headsign": "******",
                    "merged_headsign": "******",
                    "schedule_items": [
                        {
                            "departure_time": 1713461520,
                            "is_cancelled": false,
                            "is_real_time": false,
                            "rt_trip_id": "13811798",
                            "scheduled_departure_time": 1713461520,
                            "trip_search_key": "TSL:45069396:369:5:15",
                            "wheelchair_accessible": 1
                        },
                        {
                            "departure_time": 1713463320,
                            "is_cancelled": false,
                            "is_real_time": false,
                            "rt_trip_id": "13811799",
                            "scheduled_departure_time": 1713463320,
                            "trip_search_key": "TSL:45069396:369:5:16",
                            "wheelchair_accessible": 1
                        },
                        {
                            "departure_time": 1713465120,
                            "is_cancelled": false,
                            "is_real_time": false,
                            "rt_trip_id": "13811800",
                            "scheduled_departure_time": 1713465120,
                            "trip_search_key": "TSL:45069396:369:5:17",
                            "wheelchair_accessible": 1
                        }
                    ]
                }
            ],
            "mode_name": "Bus",
            "real_time_route_id": "30048",
            "route_color": "2a61a0",
            "route_long_name": "******",
            "route_network_id": "TransLink|Vancouver",
            "route_network_name": "TransLink",
            "route_short_name": "**8",
            "route_text_color": "ffffff",
            "route_type": 3,
            "sorting_key": "***",
            "tts_long_name": "*****",
            "tts_short_name": "*** "
        }
    ]
}

尝试过的错误方案 #

• 方案1：直接跳转itineraries下一项，触发list item out of range错误

if minutes < 1:
    soonestDepartureTimeUnix = (item["departure_time"] for item in tsl105513Route2["itineraries"][1]["schedule_items"])
    minutes = int((soonestDepartureTimeUnix - (time.time()))/60)

• 方案2：直接取schedule_items第二个元素，触发生成器与浮点数无法相减错误

if minutes < 1:
    soonestDepartureTimeUnix = (item["departure_time"] for item in tsl105513Route2["itineraries"][0]["schedule_items"][1])
    minutes = int((soonestDepartureTimeUnix - (time.time()))/60)

• 方案3：参考第二小值获取方案，仍返回0

if minutes < 1:
    soonestDepartureTimeUnix2 = min(item["departure_time"] for item in tsl105513Route2["itineraries"][0]["schedule_items"] if item != soonestDepartureTimeUnix)
    minutes = int((soonestDepartureTimeUnix2 - (time.time()))/60)

正确解法及错误分析 #

错误原因拆解 #

1. 方案1：itineraries数组仅包含1个元素（索引0），访问索引1必然触发越界
2. 方案2：schedule_items[1]是单个字典对象，用生成器遍历会迭代字典的键名，而非时间值，导致类型不匹配
3. 方案3：item != soonestDepartureTimeUnix是将字典与时间戳对比，结果永远为True，因此仍取到原最小值

方法1：自动筛选有效出发时间 #

提取所有出发时间并排序，依次过滤已过时间，取第一个有效且非0的时间：

import time

# 提取目标线路的所有发车时间并排序
schedule_items = tsl105513Route2["itineraries"][0]["schedule_items"]
sorted_departures = sorted(item["departure_time"] for item in schedule_items)

current_time = time.time()
target_minutes = None

for dep_time in sorted_departures:
    minutes = int((dep_time - current_time) / 60)
    if minutes > 0:
        target_minutes = minutes
        break
    elif minutes == 0:
        # 即将发车，可选择提示"即将发车"或跳过取后续车次
        continue

# 处理无后续车次的情况
if target_minutes is None:
    print("暂无后续发车班次")
else:
    print(f"下一班车还有 {target_minutes} 分钟")

方法2：针对最早时间已过的场景取第二小值 #

先获取最早时间，若已过则排除后取剩余最小值：

import time

schedule_items = tsl105513Route2["itineraries"][0]["schedule_items"]
all_departures = [item["departure_time"] for item in schedule_items]
current_time = time.time()

# 先计算最早车次的剩余时间
soonest_dep = min(all_departures)
minutes = int((soonest_dep - current_time) / 60)

# 若最早车次已过或即将发车，取第二早车次
if minutes < 1:
    remaining_departures = [t for t in all_departures if t != soonest_dep]
    if remaining_departures:
        second_soonest = min(remaining_departures)
        minutes = int((second_soonest - current_time) / 60)
    else:
        minutes = None

print(f"下一班车剩余时间：{minutes} 分钟" if minutes is not None else "暂无后续班次")

内容的提问来源于stack exchange，提问作者WesternBiscuit