用python实现的时间函数

#-*-coding:utf-8-*-
import datetime, calendar

def getYesterday():
   today=datetime.date.today()
   oneday=datetime.timedelta(days=1)
   yesterday=today-oneday 
   return yesterday
   
def getToday():
    return datetime.date.today()  

#获取给定参数的前几天的日期，返回一个list
def getDaysByNum(num):
    today=datetime.date.today()
    oneday=datetime.timedelta(days=1)    
    li=[]     
    for i in range(0,num):
        #今天减一天，一天一天减
        today=today-oneday
        #把日期转换成字符串
        #result=datetostr(today)
        li.append(datetostr(today))
    return li

#将字符串转换成datetime类型
def strtodatetime(datestr,format):    
    return datetime.datetime.strptime(datestr,format)

#时间转换成字符串,格式为2008-08-02
def datetostr(date):  
    return   str(date)[0:10]

#两个日期相隔多少天，例：2008-10-03和2008-10-01是相隔两天
def datediff(beginDate,endDate):
    format="%Y-%m-%d";
    bd=strtodatetime(beginDate,format)
    ed=strtodatetime(endDate,format)    
    oneday=datetime.timedelta(days=1)
    count=0
    while bd!=ed:
        ed=ed-oneday
        count+=1
    return count

#获取两个时间段的所有时间,返回list
def getDays(beginDate,endDate):
    format="%Y-%m-%d";
    bd=strtodatetime(beginDate,format)
    ed=strtodatetime(endDate,format)
    oneday=datetime.timedelta(days=1) 
    num=datediff(beginDate,endDate)+1 
    li=[]
    for i in range(0,num): 
        li.append(datetostr(ed))
        ed=ed-oneday
    return li

#获取当前年份 是一个字符串
def getYear():
    return str(datetime.date.today())[0:4] 

#获取当前月份 是一个字符串
def getMonth():
    return str(datetime.date.today())[5:7]

#获取当前天 是一个字符串
def getDay():
    return str(datetime.date.today())[8:10]   
def getNow():
    return datetime.datetime.now()

    
print getToday()
print getYesterday()
print getDaysByNum(3)
print getDays('2008-10-01','2008-10-05')
print '2008-10-04 00:00:00'[0:10]

print str(getYear())+getMonth()+getDay()
print getNow()