程序：

# -*- coding: UTF-8 -*-

year = int(raw_input('year:\n'))
month = int(raw_input('month:\n'))
day = int(raw_input('day:\n'))

months = (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

结果:

C:\Python27\python.exe D:/python/Four_4.py
year:
2017
month:
2
day:
14
it is the 45th day.

Process finished with exit code 0