写一个求某年某月是那一年的第几天

以下是Python代码实现：

def is_leap_year(year):
    """
    判断是否是闰年
    """
    return (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0)

def get_day_of_year(year, month, day):
    """
    计算某年某月某日是该年的第几天
    """
    days_of_month = [31, 28 + is_leap_year(year), 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]  # 每个月的天数
    day_of_year = 0
    for i in range(month - 1):
        day_of_year += days_of_month[i]
    day_of_year += day
    return day_of_year

# 测试
year = 2021
month = 7
day = 30
day_of_year = get_day_of_year(year, month, day)
print(f"{year}年{month}月{day}日是{year}年的第{day_of_year}天")

输出结果：

2021年7月30日是2021年的第211天