程序分析：3月5日为例，应该先把前两个月的加起来，然后再加上5天即本年的第几天，特殊情况，闰年且输入月份大于2时需考虑多加一天代码：
year = int(input("year:"))
month = int(input("month:"))
day = int(imput("day:"))


month = (0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334)
if 0 < month <= 12:
    sum = months[month - 1]
else:
    print("data error")
sum += day
leap = 0
if (year % 400 == 0) or (year % 4 == 0) and (year % 100 != 0):
    leap == 1
if (leap == 1) and (month > 2):
    sum += 1
print("it is the %dth day" %sum)

程序分析：3月5日为例，应该先把前两个月的加起来，然后再加上5天即本年的第几天，特殊情况，闰年且输入月份大于2时需考虑多加一天代码：
year = int(input("year:"))
month = int(input("month:"))
day = int(imput("day:"))


month = (0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334)
if 0 < month <= 12:
    sum = months[month - 1]
else:
    print("data error")
sum += day
leap = 0
if (year % 400 == 0) or (year % 4 == 0) and (year % 100 != 0):
    leap == 1
if (leap == 1) and (month > 2):
    sum += 1
print("it is the %dth day" %sum)