python-time

本文旨在记录python操作时间日期的方法，已备温故知新

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以datetime为中心，起点或中转，转化为目标对象，涵盖了大多数业务场景中需要的日期转换处理

步骤：

掌握几种对象及其关系(date，datetime，string，timetuple，timestamp)
了解每类对象的基本操作方法
通过转化关系转化

涉及对象

1. datetime

>>> import datetime
>>> now = datetime.datetime.now()
>>> now
datetime.datetime(2015, 1, 12, 23, 9, 12, 946118)

2. timestamp

>>> import time
>>> time.time()
1510889000.69805

3. time tuple

>>> import time
>>> time.localtime()
time.struct_time(tm_year=2017, tm_mon=11, tm_mday=17, tm_hour=11, tm_min=24, tm_sec=5, tm_wday=4, tm_yday=321, tm_isdst=-1)

4. string

>>> from datetime import datetime
>>> datetime.now().strftime('%Y-%m-%d %H:%M:%S')
'2017-11-17 11:27:04'

5. date

>>> from datetime import datetime
>>> datetime.now().date()
datetime.date(2017, 11, 17)

datetime基本操作

1. 获取当前datetime

>>> from datetime import datetime
>>> datetime.now()
datetime.datetime(2017, 11, 17, 11, 29, 44, 748590)

2. 获取当天date

>>> from datetime import datetime
>>> datetime.now().date()
datetime.date(2017, 11, 17)

3. 获取明天/前N天

>>> from datetime import datetime, timedelta
>>> datetime.now().date() + timedelta(days=1)
datetime.date(2017, 11, 18)
>>> datetime.now() + timedelta(days=1)
datetime.datetime(2017, 11, 18, 13, 39, 17, 495497)

4. 获取当天开始和结束时间(00:00:00 23:59:59)

>>> from datetime import datetime, time
>>> datetime.combine(datetime.now().date(), time.min)
datetime.datetime(2017, 11, 17, 0, 0)
>> datetime.combine(datetime.now().date(), time.max)
datetime.datetime(2017, 11, 17, 23, 59, 59, 999999)

5. 获取两个datetime的时间差

>>> from datetime import datetime
>>> (datetime(2017, 11, 17, 15, 0, 0) - datetime.now()).total_seconds()
4561.230405

关系转换

1. datetime <=> string

datetime -> string

>>> from datetime import datetime
>>> datetime.now().strftime('%Y-%m-%d %H:%M:%S')
'2017-11-17 13:46:28'

string -> datetime

>>> from datetime import datetime
>>> datetime.strptime('2017-11-17 13:46:28', '%Y-%m-%d %H:%M:%S')
datetime.datetime(2017, 11, 17, 13, 46, 28)

2. datetime <=> timetuple

datetime -> timetuple

>>> from datetime import datetime
>>> datetime.now().timetuple()
time.struct_time(tm_year=2017, tm_mon=11, tm_mday=17, tm_hour=13, tm_min=52, tm_sec=58, tm_wday=4, tm_yday=321, tm_isdst=-1)

timetuple -> datetime

>>> from datetime import datetime
>>> import time
>>> datetime.fromtimestamp(time.mktime(timetuple))

3. datetime <=> date

datetime -> date

>>> from datetime import datetime
>>> datetime.now().date()
datetime.date(2017, 11, 17)

date -> datetime

>>> from datetime import datetime, time
>>> today = datetime.now().date()
>>> datetime.combine(today, time())
>>> datetime.combine(today, time.max/min)

4. datetime <=> timestamp

datetime -> timestamp

>>> from datetime import datetime
>>> import time
>>> time.mktime(datetime.now().timetuple())

timestamp -> datetime

>>> from datetime import datetime
>>> datetime.fromtimestamp(1510889000.69805)
datetime.datetime(2017, 11, 17, 11, 23, 20, 698050)

python中时间的时区转换

使用python做时区转换的时候，不要使用time模块，使用datetime + pytz(第三方模块)，既方便又准确，需要记住的是，做时区转换和做进制转换差不多，一般都是先转为UTC时间，然后再互相进行转换，下面给出一个例子

arrival_nyc = '2014-05-01 23:33:24'
nyc_dt_naive = datetime.strptime(arrival_nyc, time_format)
eastern = pytz.timezone('US/Eastern')
nyc_dt = eastern.localize(nyc_dt_naive)
utc_dt = pytz.utc.normalize(nyc_dt.astimezone(pytz.utc))

pacific = pytz.timezone('US/Pacific')
sf_dt = pacific.normalize(utc_dt.astimezone(pacific))

```

python之time基础