python3: 数字日期和时间(2)

12.基本的日期与时间转换

Q: 你需要执行简单的时间转换，比如天到秒，小时到分钟等的转换

A: 为了执行不同时间单位的转换和计算，请使用 datetime 模块。 比如，为了表示一个时间段，可以创建一个 timedelta 实例，就像下面这样：

>>> from datetime import timedelta

>>> a = timedelta(days=2, hours=6)

>>> b = timedelta(hours=4.5)

>>> c = a + b

>>> c.days

2

>>> c.seconds

37800

>>> c.seconds / 3600

10.5

>>> c.total_seconds() / 3600

58.5

>>>

如果你想表示指定的日期和时间，先创建一个 datetime 实例然后使用标准的数学运算来操作它们。比如：

>>> from datetime import datetime

>>> a = datetime(2012, 9, 23)

>>> print(a + timedelta(days=10))

2012-10-03 00:00:00

>>>

>>> b = datetime(2012, 12, 21)

>>> d = b - a

>>> d.days

89

>>> now = datetime.today()

>>> print(now)

2012-12-21 14:54:43.094063

>>> print(now + timedelta(minutes=10))

2012-12-21 15:04:43.094063

>>>

#datetime会自动处理闰年

>>> a = datetime(2012, 3, 1)

>>> b = datetime(2012, 2, 28)

>>> a - b

datetime.timedelta(2)

>>> (a - b).days

2

>>> c = datetime(2013, 3, 1)

>>> d = datetime(2013, 2, 28)

>>> (c - d).days

1

>>>

13. 计算最后一个周五的日期【第三方包 python-dateutil 】

>>> from datetime import datetime

>>> from dateutil.relativedelta import relativedelta

>>> from dateutil.rrule import *

>>> d = datetime.now()

>>> print(d)

2012-12-23 16:31:52.718111

>>> # Next Friday

>>> print(d + relativedelta(weekday=FR))

2012-12-28 16:31:52.718111

>>>

>>> # Last Friday

>>> print(d + relativedelta(weekday=FR(-1)))

2012-12-21 16:31:52.718111

>>>

14. 计算当前月份的日期范围

15. 字符串转换为日期

from datetime import datetime

def parse_ymd(s):

    year_s, mon_s, day_s = s.split('-')

    return datetime(int(year_s), int(mon_s), int(day_s))

16.结合时区的日期操作