当前日期时间
 
import datetime
print datetime.datetime.now()
# 2018-05-08 16:53:30.101000
 
格式化时间
 
import datetime
print datetime.datetime.now().strftime("%Y-%m-%d %H:%M")
# 2018-05-08 16:54
 
多加一天
 
import datetime
print (datetime.datetime.now()+datetime.timedelta(days=1)).strftime("%Y-%m-%d %H:%M:%S")
# 2018-05-09 16:56:07
 
减一天
 
import datetime
print (datetime.datetime.now()+datetime.timedelta(days=-1)).strftime("%Y-%m-%d %H:%M:%S")
# 2018-05-07 16:56:59
 
其他类似
 
import datetime
in_date = '2016-08-31'
dt = datetime.datetime.strptime(in_date, "%Y-%m-%d")
out_date = (dt + datetime.timedelta(days=2)).strftime("%Y-%m-%d")
print(out_date)
# 2016-09-02
 
可以把days改为hours minutes，就可以提前XX小时/分钟了。
 
 
 
timedelta([days[, seconds[, microseconds[, milliseconds[, minutes[,
 hours[, weeks]]]]]]])
 
 
减去一年
 
import datetime
from dateutil.relativedelta import relativedelta
d = datetime.datetime.strptime('20180131', '%Y%m%d')
print(d) // 2018-01-31 00:00:00
print((d - relativedelta(years=1)).strftime('%Y%m%d')) // 20170131
 
还可以把years改为months
 
时区转换
 
from datetime import datetime
from datetime import timezone
from datetime import timedelta

# 世界标准时间
utc_time = datetime(2019, 7, 30, 7, 50, 0)

# 北京时间UTC+8
cst_time =utc_time.astimezone(timezone(timedelta(hours=-8))).strftime("%Y-%m-%d %H:%M:%S")
 
参考：
 
https://docs.python.org/2/library/datetime.html#timedelta-objects
 https://dateutil.readthedocs.io/en/stable/index.html

引入org.joda.time.DateTime
 
<dependency>
   <groupId>joda-time</groupId>
   <artifactId>joda-time</artifactId>
   <version>2.9.8</version>
</dependency>
 
1.初始化时间
 
DateTime time = new DateTime(2018,4,23,23, 7,18,888);
// 2018年4月23日23点7分18秒888毫秒  
 
2.按格式输出时间(将DateTime格式转换为字符串)
 
 String time = dateTime.toString("yyyy-MM-dd hh:mm:ss.SSSa");
 
小写hh是12小时制,大写HH是24小时制
 
3.将字符串转换为DateTime格式
 
 DateTimeFormatter format = DateTimeFormat .forPattern("yyyy-MM-dd HH:mm:ss");  
                   
 DateTime dateTime = DateTime.parse("2018-4-23 23:12:16", format); 
 
4.取得当前时间
 
DateTime time= new DateTime();
 
5.计算两个日期间隔的天数
 
 LocalDate start=new LocalDate(2018,4,23);    
 LocalDate end=new LocalDate(2019, 06, 16);    
 int days = Days.daysBetween(start, end).getDays(); 
 
6.增加日期
 
      DateTime dateTime = DateTime.parse("2018-04-23");  
                dateTime = dateTime1.plusDays(1);  
                dateTime = dateTime1.plusHours(2);  
                dateTime = dateTime1.plusMinutes(3);  
                dateTime = dateTime1.plusMonths(4);  
                dateTime = dateTime1.plusSeconds(5);  
                dateTime = dateTime1.plusWeeks(6);  
                dateTime = dateTime1.plusYears(7);  
 
7.减少日期
 
  DateTime dateTime = DateTime.parse("2018-04-23");  
                dateTime = dateTime1.minusMillis(1);  
                dateTime = dateTime1.minusHours(1);  
                dateTime = dateTime1.minusSeconds(1);;  
 
8.判断是否闰月
 
DateTime time = new DateTime();    
 org.joda.time.DateTime.Property month = time.monthOfYear();    
  System.out.println("是否闰月:" + month.isLeap());  
 
9.DateTime与Date转换
 
DateTime time = new DateTime(new Date());    
 Date date = time.toDate();    
 DateTime time2 = new DateTime(System.currentTimeMillis());    
 time2.getMillis();  
 
10.DateTime与Calendar转换
 
Calendar calendar = Calendar.getInstance();    
 dateTime = new DateTime(calendar);

from datetime import datetime
from datetime import timedelta
import time

# 1) 获取当前日期和时间
now_time = datetime.now().strftime("%Y-%m-%d %H:%M:%S")	#  此时时间年月日时分秒
now_time = time.strftime("%Y-%m-%d %H:%M:%S")	#  此时时间年月日时
today = datetime.today()    # 返回当前时间时分秒都为0
print("当前时间")
print(today)
today1 = datetime.now()  # 返回当前日期和时间
now.hour # 时
now.minute # 分
now.isoweekday（）# 返回的1-7代表周一--周日；
now.weekday（）# 返回的0-6代表周一--到周日
# 而标准格式种%w 1-6表示周一--周六，0代表周日
print( today1 )
today2 = datetime.utcnow()  # 返回当前东八区时间就是比当时时间少8个小时
print(today2)


# 2) 获取指定日期和时间,加减计算
time= datetime(2019, 5, 12, 12, 13, 14)
d= time + timedelta(weeks=0, days=0, hours=0, minutes=0,  seconds=0, milliseconds=0, microseconds=0, )		
#依次为 "周" "天", "时","分","秒","毫秒","微秒"
print(time)
print(d)

time1= "2019-5-12 12:13:14"		# 字符串 日期
d1 = datetime.strptime(str(time1),'%Y-%m-%d %H:%M:%S')
plus= d1 + timedelta(days=1)		# 加
minus = d1 - timedelta(days=1)		# 减
print(time1)
print(d1)
print(plus)
print(minus )

time2= 20190512121314
d2 = datetime.strptime(str(time2),'%Y%m%d%H%M%S')
delta = d2  + timedelta(days=1)
print(time2)
print(d2 )
print(delta)

# 3) 日期datetime-timestamp 时间戳相互转
now_stamp = time.timestamp()
print('指定时间对应时间戳 :', now_stamp)

print('对应本地时间 :', datetime.fromtimestamp(now_stamp ))
print('UTC标准时间 :', datetime.utcfromtimestamp(now_stamp ))
print('本周的第几天:', datetime.fromtimestamp(now_stamp ).weekday())


# 4) datetime 时间 转换为str字符串
now = datetime.now()
print('当前时间 :', now)
print(now.strftime('%Y%m%d%H%M%S'))

mysql 读出来的date类型的数据，在python中是datetime.date，但是通过
 
datetime.datetime.strptime(hgml+'-01','%Y-%m-%d')得到的类型是datetime.datetime类型，两者无法比较。
 
解决方法：将datetime.datetime转成datetime.date即可比较
 
datetime.datetime.date(datetime.datetime.strptime(hgml+'-01','%Y-%m-%d'))  #参数是datetime.datetime
 
 
 
 
 
另，python如何求，月初和月末
 
hgml='2020-01'
 
month_first_day = datetime.datetime.date(datetime.datetime.strptime(hgml+'-01','%Y-%m-%d'))
month_last_day = datetime.date(month_first_day.year, month_first_day.month, calendar.monthrange(month_first_day.year, month_first_day.month)[1])