如何从班次列表提取D/N班次起止日期并生成对应字典

需求规则：

• 班次为D/N时，需识别连续同类型班次的起止日期；D对应shift_type为S1，N对应S2
• W班次不计入结果，但需计算其1周的日期跨度，保证后续日期计算准确

给定输入：

shift_lst = ["D","D","D","D","N","N","W","N","N","D","D","D","D","W","N","N","N"]
current_date = date(2021, 4, 1)

待修正代码无法正确识别连续班次并计算日期，期望输出字典列表：

[
    {'shift_type': 'S1', 'start_date': '2021,4,1', 'end_date': '2021,4,4'},
    {'shift_type': 'S2', 'start_date': '2021,4,5', 'end_date': '2021,4,9'},
    {'shift_type': 'S1', 'start_date': '2021,4,11', 'end_date': '2021,4,13'}
]

from datetime import date, timedelta

shift_lst = ["D","D","D","D","N","N","W","N","N","D","D","D","D","W","N","N","N"]
current_date = date(2021, 4, 1)
result = []
current_shift = None
start_date = None

for shift in shift_lst:
    if shift == "W":
        # W班次日期+1周，同时保存之前未结束的连续班次
        current_date += timedelta(weeks=1)
        if current_shift is not None:
            end_date = current_date - timedelta(days=1)
            result.append({
                'shift_type': 'S1' if current_shift == 'D' else 'S2',
                'start_date': f"{start_date.year},{start_date.month},{start_date.day}",
                'end_date': f"{end_date.year},{end_date.month},{end_date.day}"
            })
            current_shift = None
            start_date = None
        continue
    
    # 切换班次时保存上一段连续班次数据
    if shift != current_shift:
        if current_shift is not None:
            end_date = current_date - timedelta(days=1)
            result.append({
                'shift_type': 'S1' if current_shift == 'D' else 'S2',
                'start_date': f"{start_date.year},{start_date.month},{start_date.day}",
                'end_date': f"{end_date.year},{end_date.month},{end_date.day}"
            })
        # 初始化新的连续班次跟踪
        current_shift = shift
        start_date = current_date
    
    # D/N班次日期每日递进
    current_date += timedelta(days=1)

# 处理最后一段未保存的连续班次
if current_shift is not None:
    end_date = current_date - timedelta(days=1)
    result.append({
        'shift_type': 'S1' if current_shift == 'D' else 'S2',
        'start_date': f"{start_date.year},{start_date.month},{start_date.day}",
        'end_date': f"{end_date.year},{end_date.month},{end_date.day}"
    })

# 输出结果
for item in result:
    print(item)

• 连续班次识别：用current_shift跟踪当前连续班次类型，班次切换时自动保存上一段数据
• W班次处理：直接累加1周日期，同时中断当前连续班次的跟踪并保存数据
• 日期格式化：将date对象转换为年,月,日字符串，匹配期望输出格式
• 收尾处理：循环结束后检查是否有未保存的最后一段连续班次，避免遗漏

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