Python日期格式化与健壮输入处理教程

months = [
    "January", "February", "March", "April", "May", "June",
    "July", "August", "September", "October", "November", "December"
]

while True:
    date_input = input("Date: ").strip()
    month, day, year = None, None, None # 初始化变量

    try:
        # 尝试解析 MM/DD/YYYY 或 M/D/YYYY 格式
        month_str, day_str, year_str = date_input.split("/")
        month_int = int(month_str)
        day_int = int(day_str)
        year_int = int(year_str)

        if 1 <= month_int <= 12 and 1 <= day_int <= 31:
            month = f"{month_int:02}"
            day = f"{day_int:02}"
            year = year_str
            break
    except ValueError:
        try:
            # 尝试解析 Month Day, YYYY 格式
            parts = date_input.split(" ")
            if len(parts) == 3: # 确保有三个部分
                month_name = parts[0]
                day_str = parts[1].strip(',') # 移除逗号
                year_str = parts[2]

                day_int = int(day_str)
                year_int = int(year_str)

                if month_name in months and 1 <= day_int <= 31:
                    month_index = months.index(month_name) + 1
                    month = f"{month_index:02}"
                    day = f"{day_int:02}"
                    year = year_str
                    break
        except (ValueError, IndexError):
            # 如果两种格式都解析失败，则继续循环 reprompt
            pass

print(f"{year}-{month}-{day}")

import re

months = [
    "January", "February", "March", "April", "May", "June",
    "July", "August", "September", "October", "November", "December"
]

# 定义并预编译正则表达式模式
# 匹配 M/D/YYYY 或 MM/DD/YYYY 格式，例如 9/8/1636 或 09/08/1636
FORMAT_MDY = re.compile(r"^\d{1,2}/\d{1,2}/\d{4}$")
# 匹配 Month Day, YYYY 格式，例如 September 8, 1636
FORMAT_MONTH_DAY_YEAR = re.compile(r"^[A-Za-z]+ \d{1,2}, \d{4}$")

while True:
    date_input = input("Date: ").strip()
    month_val = None
    day_val = None
    year_val = None

    if FORMAT_MDY.match(date_input):
        # 输入匹配 M/D/YYYY 格式
        try:
            month_str, day_str, year_str = date_input.split("/")
            month_int = int(month_str)
            day_int = int(day_str)
            year_int = int(year_str)

            # 进一步验证日期范围
            if 1 <= month_int <= 12 and 1 <= day_int <= 31:
                month_val = f"{month_int:02}"
                day_val = f"{day_int:02}"
                year_val = year_str
                break # 成功解析，退出循环
            else:
                print("Invalid month or day range.")
        except ValueError:
            # 理论上，如果regex匹配，这里不应出现ValueError，但作为安全措施保留
            print("Parsing error after regex match (MDY format).")
            pass # 重新提示输入

    elif FORMAT_MONTH_DAY_YEAR.match(date_input):
        # 输入匹配 Month Day, YYYY 格式
        try:
            # 使用空格分割，然后处理日期部分的逗号
            parts = date_input.split(" ")
            month_name = parts[0]
            day_str = parts[1].strip(',') # 此时因为regex已验证，可以确定有逗号
            year_str = parts[2]

            day_int = int(day_str)
            year_int = int(year_str)

            # 进一步验证月份名称和日期范围
            if month_name in months and 1 <= day_int <= 31:
                month_index = months.index(month_name) + 1
                month_val = f"{month_index:02}"
                day_val = f"{day_int:02}"
                year_val = year_str
                break # 成功解析，退出循环
            else:
                print("Invalid month name or day range.")
        except (ValueError, IndexError):
            print("Parsing error after regex match (Month Day, YYYY format).")
            pass # 重新提示输入
    else:
        # 任何模式都不匹配，提示用户重新输入
        print("Invalid date format. Please use MM/DD/YYYY or Month Day, YYYY.")

# 输出标准化后的日期
print(f"{year_val}-{month_val}-{day_val}")