处理不同长度的日期字符串

from datetime import datetime

def parse_date(date_str):
    date_formats = {
        8: "%Y%m%d",
        10: "%Y-%m-%d",
        16: "%Y-%m-%d %H:%M",
        19: "%Y-%m-%d %H:%M:%S"
    }
    
    try:
        date_format = date_formats[len(date_str)]
        date_obj = datetime.strptime(date_str, date_format)
        return date_obj
    except KeyError:
        return None

# 示例用法
date_str_1 = "20220101"
date_obj_1 = parse_date(date_str_1)
print(date_obj_1)  # 输出：2022-01-01 00:00:00

date_str_2 = "2022-01-01"
date_obj_2 = parse_date(date_str_2)
print(date_obj_2)  # 输出：2022-01-01 00:00:00

date_str_3 = "2022-01-01 12:34"
date_obj_3 = parse_date(date_str_3)
print(date_obj_3)  # 输出：2022-01-01 12:34:00

date_str_4 = "2022-01-01 12:34:56"
date_obj_4 = parse_date(date_str_4)
print(date_obj_4)  # 输出：2022-01-01 12:34:56