Python新手求助：Pytest测试时间转换函数时出现ValueError异常

作为Python新手，我编写了一个12小时制转24小时制的时间格式转换函数，尝试用try-except捕获ValueError，同时通过条件语句处理错误场景。函数代码如下：

import re


def main():
    print(convert(input("Hours: ")))


def convert(s):
    try:
        # matches := re.search(r"^(\d+)\:?(.+)? to (\d+)\:?(.+)?$", s)
        if (matches := re.search(r"^(\d+)\:?(.+)? to (\d+)\:?(.+)?$", s)) and s.__contains__("AM"):
            matchesGroup1 = matches.group(1)
            matchesGroup2 = matches.group(2).split(" ")
            matchesGroup3 = matches.group(3)
            matchesGroup4 = matches.group(4).split(" ")

            if 0 < int(matches.group(1)) <= 12 and 0 < int(matches.group(3)) <= 12:

                if matchesGroup2[1] == "AM" and matchesGroup4[1] == "PM":
                    if matchesGroup1 == "12" and matchesGroup3 == "12":
                        matchesGroup1 = "00"
                        matchesGroup3 = "12"
                    else:
                        matchesGroup3 = int(matchesGroup3) + 12
                        matchesGroup1 = "0" + matchesGroup1
                else:
                    if matchesGroup1 == "12" and matchesGroup3 == "12":
                        matchesGroup3 = "12"
                        matchesGroup1 = "00"
                    else:
                        matchesGroup1 = int(matchesGroup1) + 12
                        matchesGroup3 = "0" + matchesGroup3

                if len(matchesGroup2[0]) == 0 and len(matchesGroup4[0]) == 0:
                    matchesGroup2[0] += "00"
                    matchesGroup4[0] += "00"
                elif "00" <= matchesGroup2[0] <= "59" and "00" <= matchesGroup4[0] <= "59":
                    pass
                else:
                    raise Exception

                return f"{matchesGroup1}:{matchesGroup2[0]} to {matchesGroup3}:{matchesGroup4[0]}"

        else:
            raise Exception

    except Exception:
        raise ValueError
    except ValueError:
        raise ValueError


if __name__ == "__main__":
    main()

我用Pytest编写了测试用例：

import pytest
from working import convert

def test_convert():
    assert convert("9 AM to 5 PM") == "09:00 to 17:00"
    assert convert("9:00 AM to 5:00 PM") == "09:00 to 17:00"
    assert convert("10 PM to 8 AM") == "22:00 to 08:00"
    assert convert("10:30 PM to 8:50 AM") == "22:30 to 08:50"
    assert convert("9:00 AM 5:00 PM") == ValueError

但测试最后一个用例时抛出异常，提示working.py:45: Exception、test_working.py:9:、working.py:48: ValueError，需要分析异常原因并给出修复方案。

1. 正则匹配失败触发异常：最后一个测试用例"9:00 AM 5:00 PM"中没有关键字to，不符合函数里正则表达式^(\d+)\:?(.+)? to (\d+)\:?(.+)?$的匹配规则，导致matches为None，进入else分支抛出Exception，随后被except Exception捕获并转抛ValueError。
2. 测试用例写法错误：断言函数抛出异常不能用== ValueError，这种写法是在判断函数返回值是否等于ValueError类对象，但实际函数会直接抛出异常而非返回该对象，因此pytest会捕获到这个未预期的异常，判定测试失败。
3. 原函数逻辑存在其他漏洞：
   • 仅判断输入包含AM，如果输入是全PM的格式（如"1 PM to 2 PM"）会直接触发异常。
   • 用字符串比较分钟范围（"00" <= matchesGroup2[0] <= "59"），虽然部分场景有效，但逻辑不严谨，比如"60"作为字符串会被误判为合法。
   • 12小时转24小时的逻辑仅覆盖了前AM后PM、前PM后AM的同时12点场景，其他边界情况（如"12 AM to 1 PM"）会生成错误的时间格式（如"012:00"）。

1. 修复测试用例 #

使用pytest的pytest.raises上下文管理器来断言函数抛出异常，拆分测试用例为合法格式和非法格式两类：

import pytest
from working import convert

def test_convert_valid():
    assert convert("9 AM to 5 PM") == "09:00 to 17:00"
    assert convert("9:00 AM to 5:00 PM") == "09:00 to 17:00"
    assert convert("10 PM to 8 AM") == "22:00 to 08:00"
    assert convert("10:30 PM to 8:50 AM") == "22:30 to 08:50"
    assert convert("12 AM to 12 PM") == "00:00 to 12:00"
    assert convert("12:30 PM to 12:30 AM") == "12:30 to 00:30"

def test_convert_invalid():
    # 缺少to的情况
    with pytest.raises(ValueError):
        convert("9:00 AM 5:00 PM")
    # 小时超出范围
    with pytest.raises(ValueError):
        convert("13 AM to 5 PM")
    # 分钟超出范围
    with pytest.raises(ValueError):
        convert("9:60 AM to 5 PM")
    # 格式错误
    with pytest.raises(ValueError):
        convert("9 AM 5 PM")

2. 重构转换函数 #

优化正则表达式、拆分转换逻辑、简化异常处理，修复所有逻辑漏洞：

import re

def main():
    print(convert(input("Hours: ")))

def convert_12_to_24(hour: str, minute: str | None, period: str) -> str:
    """将12小时制的小时、分钟、时段转换为24小时制的时间字符串"""
    hour_int = int(hour)
    # 处理分钟，默认补00
    minute_str = minute if minute is not None else "00"
    minute_int = int(minute_str)
    
    # 验证分钟合法性
    if not 0 <= minute_int <= 59:
        raise ValueError
    # 转换小时
    if period == "AM":
        hour_str = "00" if hour_int == 12 else f"{hour_int:02d}"
    else:  # PM
        hour_str = "12" if hour_int == 12 else f"{hour_int + 12:02d}"
    
    return f"{hour_str}:{minute_str}"

def convert(s: str) -> str:
    # 精准匹配12小时制时间格式：小时(1-2位) + 可选分钟(两位) + AM/PM + to + 结束时间
    pattern = r"^(\d{1,2})(?:\:(\d{2}))? (AM|PM) to (\d{1,2})(?:\:(\d{2}))? (AM|PM)$"
    matches = re.search(pattern, s)
    
    if not matches:
        raise ValueError
    
    start_hour = matches.group(1)
    start_minute = matches.group(2)
    start_period = matches.group(3)
    end_hour = matches.group(4)
    end_minute = matches.group(5)
    end_period = matches.group(6)
    
    # 验证小时合法性
    start_hour_int = int(start_hour)
    end_hour_int = int(end_hour)
    if not (1 <= start_hour_int <= 12) or not (1 <= end_hour_int <= 12):
        raise ValueError
    
    # 转换开始和结束时间
    start_24 = convert_12_to_24(start_hour, start_minute, start_period)
    end_24 = convert_12_to_24(end_hour, end_minute, end_period)
    
    return f"{start_24} to {end_24}"

if __name__ == "__main__":
    main()

修复要点说明 #

• 正则表达式优化：使用(\d{1,2})匹配1-2位小时，(?:\:(\d{2}))?匹配可选的两位分钟（非捕获组），确保输入格式严格符合要求。
• 拆分转换逻辑：将12小时转24小时的逻辑抽离为辅助函数，代码更清晰，便于维护和测试。
• 数值验证：所有时间数值（小时、分钟）转成整数后再做范围判断，避免字符串比较的逻辑漏洞。
• 简化异常处理：直接在不符合条件时抛出ValueError，无需捕获Exception再转抛，逻辑更直接。

内容的提问来源于stack exchange，提问作者Navfalbek