Python strftime 和 strptime

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时间转字符串（格式化） 用strftime format

>>> from datetime import datetime
>>> datetime.now().strftime('%Y-%m-%d %H:%M:%S')
'2019-09-27 12:58:36'

字符串转时间（解析） 用strptime parse

>>> from datetime import datetime
>>> datetime.strptime("2019-09-27 13:03:09", "%Y-%m-%d %H:%M:%S")
datetime.datetime(2019, 9, 27, 13, 3, 9)

datetime 模块的使用 搬砖 ↓ 
1. 获取当前datetime

>>> import datetime
>>> datetime.datetime.now()
datetime.datetime(2015, 1, 12, 23, 26, 24, 475680)

2. 获取当天date

>>> datetime.date.today()
datetime.date(2015, 1, 12)

3. 获取明天/前N天 
明天

>>> datetime.date.today() + datetime.timedelta(days=1)
datetime.date(2015, 1, 13)

三天前

>>> datetime.datetime.now()
datetime.datetime(2015, 1, 12, 23, 38, 55, 492226)
>>> datetime.datetime.now() - datetime.timedelta(days=3)
datetime.datetime(2015, 1, 9, 23, 38, 57, 59363)

4. 获取当天开始和结束时间(00:00:00 23:59:59)

>>> datetime.datetime.combine(datetime.date.today(), datetime.time.min)
datetime.datetime(2015, 1, 12, 0, 0)
>>> datetime.datetime.combine(datetime.date.today(), datetime.time.max)
datetime.datetime(2015, 1, 12, 23, 59, 59, 999999)

5. 获取两个datetime的时间差

>>> (datetime.datetime(2015,1,13,12,0,0) - datetime.datetime.now()).total_seconds()
44747.768075

6. 获取本周/本月/上月最后一天 
本周

>>> today = datetime.date.today()
>>> today
datetime.date(2015, 1, 12)
>>> sunday = today + datetime.timedelta(6 - today.weekday())
>>> sunday
datetime.date(2015, 1, 18)

本月

>>> import calendar
>>> today = datetime.date.today()
>>> _, last_day_num = calendar.monthrange(today.year, today.month)
>>> last_day = datetime.date(today.year, today.month, last_day_num)
>>> last_day
datetime.date(2015, 1, 31)

获取上个月的最后一天(可能跨年)

>>> import datetime
>>> today = datetime.date.today()
>>> first = datetime.date(day=1, month=today.month, year=today.year)
>>> lastMonth = first - datetime.timedelta(days=1)

关系转换 
几个关系之间的转化

Datetime Object / String / timestamp / time tuple

关系转换例子 
datetime <=> string 
datetime -> string

>>> import datetime
>>> datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
'2015-01-12 23:13:08'

string -> datetime

>>> import datetime
>>> datetime.datetime.strptime("2014-12-31 18:20:10", "%Y-%m-%d %H:%M:%S")
datetime.datetime(2014, 12, 31, 18, 20, 10)

datetime <=> timetuple 
datetime -> timetuple

>>> import datetime
>>> datetime.datetime.now().timetuple()
time.struct_time(tm_year=2015, tm_mon=1, tm_mday=12, tm_hour=23, tm_min=17, tm_sec=59, tm_wday=0, tm_yday=12, tm_isdst=-1)

timetuple -> datetime

timetuple => timestamp => datetime [看后面 
datetime<=>timestamp] 
datetime <=> date 
datetime -> date

>>> import datetime
>>> datetime.datetime.now().date()
datetime.date(2015, 1, 12)

date -> datetime

>>> datetime.date.today()
datetime.date(2015, 1, 12)
>>> today = datetime.date.today()
>>> datetime.datetime.combine(today, datetime.time())
datetime.datetime(2015, 1, 12, 0, 0)
>>> datetime.datetime.combine(today, datetime.time.min)
datetime.datetime(2015, 1, 12, 0, 0)

datetime <=> timestamp 
datetime -> timestamp

>>> now = datetime.datetime.now()
>>> timestamp = time.mktime(now.timetuple())
>>> timestamp
1421077403.0

timestamp -> datetime

>>> datetime.datetime.fromtimestamp(1421077403.0)
datetime.datetime(2015, 1, 12, 23, 43, 23)

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