方法一：

"""

3、输入某年某月某日，判断这一天是这一年的第几天

"""

year = int(input("请输入年分："))

month = int(input("请输入月份："))

day = int(input("请输入日："))

count = 0

if month == 1:

count = day

elif month == 2:

count = 31 + day

elif month == 3 and ((year % 4 == 0 and year % 100 != 0) or (year % 400 == 0)):

if month == 3:

count = 31 + 29 + day

if month == 4:

count = 31 + 29 + 31 + day

if month == 5:

count = 31 + 29 + 31 + 30 + day

if month == 6:

count = 31 + 29 + 31 + 30 + 31 + day

if month == 7:

count = 31 + 29 + 31 + 30 + 31 + 30 + day

if month == 8:

count = 31 + 29 + 31 + 30 + 31 + 30 + 31 + day

if month == 9:

count = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + day

if month == 10:

count = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + day

if month == 11:

count = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + day

if month == 12:

count = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + day

else:

if month == 3:

count = 31 + 28 + day

if month == 4:

count = 31 + 28 + 31 + day

if month == 5:

count = 31 + 28 + 31 + 30 + day

if month == 6:

count = 31 + 28 + 31 + 30 + 31 + day

if month == 7:

count = 31 + 28 + 31 + 30 + 31 + 30 + day

if month == 8:

count = 31 + 28 + 31 + 30 + 31 + 30 + 31 + day

if month == 9:

count = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + day

if month == 10:

count = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + day

if month == 11:

count = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + day

if month == 12:

count = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + day

print("公共%d天" % count)

方法二：

print("-" * 20)

import datetime

result = datetime.datetime(year, month, day)

# 用来格式化时间，%j 用来表示天数

print(result.strftime("%j"))

方法三：

"""

3、输入某年某月某日，判断这一天是这一年的第几天

"""

year = int(input("请输入年分："))

month = int(input("请输入月份："))

day = int(input("请输入日："))

print("-" * 20)

day += (month-1) * 30

if month < 9:

day += month//2

else:

day += (month+1)//2

if month > 2:

if year%400 ==0 or year%4 == 0 and year%100 !=0 :

day -= 1

else:

day -= 2

print("是一年的第%d天"%day)