python：日期计算

蔡文勇 發表於 2019-10-15 18:07:00

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：
<img src="https://img2018.cnblogs.com/blog/867526/201910/867526-20191015180356162-88628016.png">
 
第一步，利用datetime模块获取当前日期 datetime.date.today(); 如下图所示：
<img src="https://img2018.cnblogs.com/blog/867526/201910/867526-20191015180440935-323605705.png">
 
 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：
<img src="https://img2018.cnblogs.com/blog/867526/201910/867526-20191015180517251-1214048588.png">
 
 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：
<img src="https://img2018.cnblogs.com/blog/867526/201910/867526-20191015180543681-804106795.png">
 
 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：
<img src="https://img2018.cnblogs.com/blog/867526/201910/867526-20191015180610585-1612885993.png">
 
 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：
<img src="https://img2018.cnblogs.com/blog/867526/201910/867526-20191015180640229-1163643110.png">
 
 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：
<img src="https://img2018.cnblogs.com/blog/867526/201910/867526-20191015180704986-1737810530.png">
 
 
 
<div class="cnblogs_code">
<pre># -*- 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)

def get_firstday_of_month(year, mon):
'''''
get the first day of month
date format = "YYYY-MM-DD"
'''
days = "01"
if (int(mon) < 10):
 mon = "0" + 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)
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 = "01"
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):
 return "0" + 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 todaystr()#20171202
print datetime()#2017-12-02 16:37:19
print datetimestr()#20171202163719
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</pre>
</div>
  
来源：https://www.cnblogs.com/gcgc/p/11679376.html

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python：日期计算