from datetime import datetime, date

if __name__ == '__main__':
    text = "2012-09-20"

    # str -> time
    y = datetime.strptime(text, "%Y-%m-%d")
    z = datetime.now()
    diff = z - y
    print(diff)

    # 如果你觉得不够美观，那就格式化一下
    # time -> str
    struct_time_str = datetime.strftime(y, "%A %B %d, %Y")
    print(struct_time_str)

    # 当然，strptime这个函数的性能相当糟糕，大量使用时如果考虑到效率问题还请自己动手
    def parse_date(date_str):
        y, m, d = date_str.split("-")
        return datetime(int(y), int(m), int(d))

    print(parse_date(text))