一， datetime
1. datetime是Python处理日期和时间的标准库
2. from datetime import datetime
datetime是模块，该模块还包含一个datetime类。
3.常用操作：
>>> from datetime import datetime
>>> #获取当前日期和时间
>>> now=datetime.now()
>>> print(now)
2019-03-12 08:48:56.186838
>>> print(type(now))
<class 'datetime.datetime'>
>>> #通过参数指定某个日期和时间
>>> dt=datetime(2015,4,19,12,20,12)
>>> print(dt)
2015-04-19 12:20:12
>>> #将datetime类型转换为timestamp
>>> dt.timestamp()
1429417212.0
>>> #将timestamp类型转换为datetime
>>> ts=dt.timestamp()
>>> print(datetime.fromtimestamp(ts))
2015-04-19 12:20:12
>>> #将timestamp转换为UTC标准时区时间
>>> print(datetime.utcfromtimestamp(ts))
2015-04-19 04:20:12
>>> #将字符串处理为datetiem类型
>>> cday=datetime.strptime('2015-6-1 18:19:59','%Y-%m-%d %H:%M:%S')
>>> print(cday)
2015-06-01 18:19:59
>>> #将datetime 转换为 str
>>> now=datetime.now()
>>> print(now.strftime('%a,%b %d %H:%M'))
Tue,Mar 12 09:05
>>> #对日期时间进行加减
>>> from datetime import datetime,timedelta
>>> now+timedelta(hours=10)
datetime.datetime(2019, 3, 12, 19, 5, 12, 894703)
>>> now-timedelta(days=1)
datetime.datetime(2019, 3, 11, 9, 5, 12, 894703)
>>> #本地时间转换为UTC时间
>>> #datetime类型有个时区属性tzinfo
>>> from datetime import datetime,timedelta,timezone
>>> tz_utc_8=timezone(timedelta(hours=8))
>>> now
datetime.datetime(2019, 3, 12, 9, 5, 12, 894703)
>>> dt=now.replace(tzinfo=tz_utc_8)
>>> dt
datetime.datetime(2019, 3, 12, 9, 5, 12, 894703, tzinfo=datetime.timezone(datetime.timedelta(0, 28800)))
>>> #时区转换
>>> #一般做法是先拿到当前的UTC时间，再转换为任意时区的时间
>>> utc_dt=datetime.utcnow().replace(tzinfo=timezone.utc)
>>> print(utc_dt)
2019-03-12 01:13:31.002193+00:00
>>> #转换时区为北京时间
>>> bj_dt=utc_dt.astimezone(timezone(timedelta(hours=8)))
>>> print(bj_dt)
2019-03-12 09:13:31.002193+08:00
>>>