import time

时间相关的操作，时间有三种表示方式：

• 时间戳               1970年1月1日之后的秒，即：time.time()
• 格式化的字符串    2014-11-11 11:11，    即：time.strftime('%Y-%m-%d')
• 结构化时间          元组包含了：年、日、星期等... time.struct_time    即：time.localtime()

 print time.time()
 print time.mktime(time.localtime())
    
 print time.gmtime()    #可加时间戳参数
 print time.localtime() #可加时间戳参数
 print time.strptime('2014-11-11', '%Y-%m-%d')
    
 print time.strftime('%Y-%m-%d') #默认当前时间
 print time.strftime('%Y-%m-%d',time.localtime()) #默认当前时间
 print time.asctime()
 print time.asctime(time.localtime())
 print time.ctime(time.time())
    
 import datetime
 '''
 datetime.date：表示日期的类。常用的属性有year, month, day
 datetime.time：表示时间的类。常用的属性有hour, minute, second, microsecond
 datetime.datetime：表示日期时间
 datetime.timedelta：表示时间间隔，即两个时间点之间的长度
 timedelta([days[, seconds[, microseconds[, milliseconds[, minutes[, hours[, weeks]]]]]]])
 strftime("%Y-%m-%d")
 '''
 import datetime
 print datetime.datetime.now()
 print datetime.datetime.now() - datetime.timedelta(days=5)

%Y  Year with century as a decimal number.
    %m  Month as a decimal number [01,12].
    %d  Day of the month as a decimal number [01,31].
    %H  Hour (24-hour clock) as a decimal number [00,23].
    %M  Minute as a decimal number [00,59].
    %S  Second as a decimal number [00,61].
    %z  Time zone offset from UTC.
    %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.
    %I  Hour (12-hour clock) as a decimal number [01,12].
    %p  Locale's equivalent of either AM or PM.

格式化占位符