Python 时间日期格式定义：

In [104]: time.strftime("%H:%M:%S",time.localtime())

Out[104]: '12:04:36'

In [105]: time.strftime("%Y-%m-%d",time.localtime())

Out[105]: '2011-06-07'

In [107]: time.strftime("%Y-%m-%d %H:%M:%S",time.localtime())

Out[107]: '2011-06-07 12:09:21'

In [121]: time.strftime("%Y-%m-%y %H:%M:%S",time.gmtime())

Out[121]: '2011-06-11 04:17:28'

localtime返回tuple格式的时间，有一个和它类似的函数叫gmtime(),2个函数的差别是时区，gmtime()返回的是0时区的值，localtime返回的是当前时区的值。

ISOFORMAT：

In [106]: datetime.date.today().isoformat()

Out[106]: '2011-06-07'

参考：

%a	Locale’s abbreviated weekday name.
%A	Locale’s full weekday name.
%b	Locale’s abbreviated month name.
%B	Locale’s full month name.
%c	Locale’s appropriate date and time representation.
%d	Day of the month as a decimal number [01,31].
%H	Hour (24-hour clock) as a decimal number [00,23].
%I	Hour (12-hour clock) as a decimal number [01,12].
%j	Day of the year as a decimal number [001,366].
%m	Month as a decimal number [01,12].
%M	Minute as a decimal number [00,59].
%p	Locale’s equivalent of either AM or PM.	(1)
%S	Second as a decimal number [00,61].	(2)
%U	Week number of the year (Sunday as the first day of the week) as a decimal number [00,53]. All days in a new year preceding the first Sunday are considered to be in week 0.	(3)
%w	Weekday as a decimal number [0(Sunday),6].
%W	Week number of the year (Monday as the first day of the week) as a decimal number [00,53]. All days in a new year preceding the first Monday are considered to be in week 0.	(3)
%x	Locale’s appropriate date representation.
%X	Locale’s appropriate time representation.
%y	Year without century as a decimal number [00,99].
%Y	Year with century as a decimal number.
%Z	Time zone name (no characters if no time zone exists).
%%	A literal '%' character.