Python常用模块：datetime

>>> from datetime import datetime

>>> now = datetime.now() # 获取当前datetime
>>> print(now)
2015-05-18 16:28:07.198690

>>> from datetime import datetime
>>> dt = datetime(2015, 4, 19, 12, 20) # 用指定日期时间创建datetime
>>> print(dt)
2015-04-19 12:20:00

>>> from datetime import datetime
>>> dt = datetime(2015, 4, 19, 12, 20) # 用指定日期时间创建datetime
>>> dt.timestamp() # 把datetime转换为timestamp
1429417200.0

>>> from datetime import datetime
>>> t = 1429417200.0
>>> print(datetime.fromtimestamp(t))
2015-04-19 12:20:00

很多时候，用户输入的日期和时间是字符串，要处理日期和时间，首先必须把str转换为datetime。转换方法是通过datetime.strptime()实现，需要一个日期和时间的格式化字符串：

>>> from datetime import datetime
>>> cday = datetime.strptime('2015-6-1 18:19:59', '%Y-%m-%d %H:%M:%S')
>>> print(cday)
2015-06-01 18:19:59
字符串'%Y-%m-%d %H:%M:%S'规定了日期和时间部分的格式

datetime转换为str

如果已经有了datetime对象，要把它格式化为字符串显示给用户，就需要转换为str，转换方法是通过strftime()实现的，同样需要一个日期和时间的格式化字符串：

>>> from datetime import datetime
>>> now = datetime.now()
>>> print(now.strftime('%a, %b %d %H:%M'))
Mon, May 05 16:28

>>> from datetime import datetime, timedelta
>>> now = datetime.now()
>>> now
datetime.datetime(2015, 5, 18, 16, 57, 3, 540997)
>>> now + timedelta(hours=10)
datetime.datetime(2015, 5, 19, 2, 57, 3, 540997)
>>> now - timedelta(days=1)
datetime.datetime(2015, 5, 17, 16, 57, 3, 540997)
>>> now + timedelta(days=2, hours=12)
datetime.datetime(2015, 5, 21, 4, 57, 3, 540997)