python获取日期加减之后的日期

python语言中的datetime模块可以利用其中的方法获取不同的日期，比如获取当前日期、明天、昨天、上个月、下个月和明年。下面利用几个实例说明这些日期的获取方法，操作如下：

 

 

第一步，利用datetime模块获取当前日期
datetime.date.today();
如下图所示：

 

 

第二步，获取当前日期前一天日期，利用当前日期减去一天，如下图所示：

 

 

第三步，获取当前日期后一天日期，利用当前日期加上一天，如下图所示：

 

 

第四步，获取当前日期下一个月日期，利用当前日期加上30天，如下图所示：

 

 

第五步，获取当前日期上一个月的日期，利用当前日期减去30天，如下图所示：

 

 

第六步，获取当前日期返回明年今天的日期，利用当前日期加上365天，如下图所示：

 

 

• python获取前后N天或前后N个月的日期

   # -*- coding: utf-8 -*-
  
   #-----------------------------------------------------------------------------------
   import datetime
   #获取366天前的日期
   day=(datetime.date.today() - datetime.timedelta(days=366)).strftime('%Y-%m-%d')
   print(day)
   #获取366天后的日期
   day=(datetime.date.today() + datetime.timedelta(days=366)).strftime('%Y-%m-%d')
   print(day)
   #3周前期
   day=(datetime.date.today() + datetime.timedelta(weeks=-3)).strftime('%Y-%m-%d')
   print(day)
   #-----------------------------------------------------------------------------------
  
   '''获取当前日期前后N天或N月的日期'''
  
   from time import strftime, localtime
   from datetime import timedelta, date
   import calendar
  
   year = strftime("%Y", localtime())
   mon = strftime("%m", localtime())
   day = strftime("%d", localtime())
   hour = strftime("%H", localtime())
   min = strftime("%M", localtime())
   sec = strftime("%S", localtime())
  
   def today():
       '''''
       get today,date format="YYYY-MM-DD"
       '''''
       return date.today()
  
   def todaystr():
       '''
       get date string, date format="YYYYMMDD"
       '''
       return year + mon + day
  
   def datetime():
       '''''
       get datetime,format="YYYY-MM-DD HH:MM:SS"
       '''
       return strftime("%Y-%m-%d %H:%M:%S", localtime())
  
   def datetimestr():
       '''''
       get datetime string
       date format="YYYYMMDDHHMMSS"
       '''
       return year + mon + day + hour + min + sec
  
   def get_day_of_day(n=0):
       '''''
       if n>=0,date is larger than today
       if n<0,date is less than today
       date format = "YYYY-MM-DD"
       '''
       if (n < 0):
           n = abs(n)
           return date.today() - timedelta(days=n)
       else:
           return date.today() + timedelta(days=n)
  
   def get_days_of_month(year, mon):
       '''''
       get days of month
       '''
       return calendar.monthrange(year, mon)[1]
  
   def get_firstday_of_month(year, mon):
       '''''
       get the first day of month
       date format = "YYYY-MM-DD"
       '''
       days = "
       if (int(mon) < 10):
           mon = " + str(int(mon))
       arr = (year, mon, days)
       return "-".join("%s" % i for i in arr)
  
   def get_lastday_of_month(year, mon):
       '''''
       get the last day of month
       date format = "YYYY-MM-DD"
       '''
       days = calendar.monthrange(year, mon)[1]
       mon = addzero(mon)
       arr = (year, mon, days)
       return "-".join("%s" % i for i in arr)
  
   def get_firstday_month(n=0):
       '''''
       get the first day of month from today
       n is how many months
       '''
       (y, m, d) = getyearandmonth(n)
       d = "
       arr = (y, m, d)
       return "-".join("%s" % i for i in arr)
  
   def get_lastday_month(n=0):
       '''''
       get the last day of month from today
       n is how many months
       '''
       return "-".join("%s" % i for i in getyearandmonth(n))
  
   def getyearandmonth(n=0):
       '''''
       get the year,month,days from today
       befor or after n months
       '''
       thisyear = int(year)
       thismon = int(mon)
       totalmon = thismon + n
       if (n >= 0):
           if (totalmon <= 12):
               days = str(get_days_of_month(thisyear, totalmon))
               totalmon = addzero(totalmon)
               return (year, totalmon, days)
           else:
               i = totalmon / 12
               j = totalmon % 12
               if (j == 0):
                   i -= 1
                   j = 12
               thisyear += i
               days = str(get_days_of_month(thisyear, j))
               j = addzero(j)
               return (str(thisyear), str(j), days)
       else:
           if ((totalmon > 0) and (totalmon < 12)):
               days = str(get_days_of_month(thisyear, totalmon))
               totalmon = addzero(totalmon)
               return (year, totalmon, days)
           else:
               i = totalmon / 12
               j = totalmon % 12
               if (j == 0):
                   i -= 1
                   j = 12
               thisyear += i
               days = str(get_days_of_month(thisyear, j))
               j = addzero(j)
               return (str(thisyear), str(j), days)
  
   def addzero(n):
       '''''
       add 0 before 0-9
       return 01-09
       '''
       nabs = abs(int(n))
       if (nabs < 10):
           " + str(nabs)
       else:
           return nabs
  
   def get_today_month(n=0):
       '''''
       获取当前日期前后N月的日期
       if n>0, 获取当前日期前N月的日期
       if n<0, 获取当前日期后N月的日期
       date format = "YYYY-MM-DD"
       '''
       (y, m, d) = getyearandmonth(n)
       arr = (y, m, d)
       if (int(day) < int(d)):
           arr = (y, m, day)
       return "-".join("%s" % i for i in arr)
  
   if __name__ == "__main__":
       print today()#获取当前日期，2017-12-02
  
       print datetime()#2017-12-02 16:37:19
  
       print get_day_of_day(20)#获取20天后的日期，2017-12-22
       print get_day_of_day(-3)#获取3天前的日期，2017-11-29
       print get_today_month(-3)#获取3个月前的日期，  2017-09-02
       print get_today_month(3)# 获取3个月后的日期， 2018-03-02
       print get_today_month(19)# 获取19个月后的日期，2019-07-02