如何在Django中舍入一个具有时区意识的日期

Question

我试图将默认时区datetime转换为localtime，并在Django视图中将时间调整为15分钟。我有以下roundTime函数:

def roundTime(dt=None, dateDelta=timedelta(minutes=1)):
    """Round a datetime object to a multiple of a timedelta
    dt : datetime.datetime object, default now.
    dateDelta : timedelta object, we round to a multiple of this, default 1 minute.
    Author: Thierry Husson 2012 - Use it as you want but don't blame me.
            Stijn Nevens 2014 - Changed to use only datetime objects as variables
    """
    roundTo = dateDelta.total_seconds()
    if dt == None:
        dt = datetime.now()
    seconds = (dt - dt.min).seconds
    # // is a floor division, not a comment on following line:
    rounding = (seconds+roundTo/2) // roundTo * roundTo
    return dt + timedelta(0,rounding-seconds,-dt.microsecond)

以下是我目前为止所做的尝试:

mytime = roundTime(datetime.now(),timedelta(minutes=15)).strftime('%H:%M:%S') #works OK
mytime = datetime.strptime(str(mytime), '%H:%M:%S') #works OK
mytime = timezone.localtime(mytime) 

但是最后一行给了我这个错误:

error: astimezone()不能应用于初始日期时间

当我使用:

local_time = timezone.localtime(timezone.now()) 

我确实得到了正确的当地时间，但由于某种原因，我无法通过执行

来四舍五入时间:

mytime = roundTime(local_time,timedelta(minutes=15)).strftime('%H:%M:%S') 

与上面的datetime.now()一起工作。

我能够想出这个不漂亮但工作的代码:

mytime = timezone.localtime(timezone.now())
mytime = datetime.strftime(mytime, '%Y-%m-%d %H:%M:%S')
mytime = datetime.strptime(str(mytime), '%Y-%m-%d %H:%M:%S')
mytime = roundTime(mytime,timedelta(minutes=15)).strftime('%H:%M:%S')
mytime = datetime.strptime(str(mytime), '%H:%M:%S')

有更好的解决方案吗?

Answer 1

您正在使用的roundTime函数不适用于具有时区意识的日期。为了支持它，您可以这样修改它:

def roundTime(dt=None, dateDelta=timedelta(minutes=1)):
    """Round a datetime object to a multiple of a timedelta
    dt : datetime.datetime object, default now.
    dateDelta : timedelta object, we round to a multiple of this, default 1 minute.
    Author: Thierry Husson 2012 - Use it as you want but don't blame me.
            Stijn Nevens 2014 - Changed to use only datetime objects as variables
    """
    roundTo = dateDelta.total_seconds()
    if dt == None : 
        dt = datetime.now()
    #Make sure dt and datetime.min have the same timezone
    tzmin = dt.min.replace(tzinfo=dt.tzinfo)
    seconds = (dt - tzmin).seconds
    # // is a floor division, not a comment on following line:
    rounding = (seconds+roundTo/2) // roundTo * roundTo
    return dt + timedelta(0,rounding-seconds,-dt.microsecond)

这样，函数就可以同时处理朴素日期和z感知日期。然后，您可以像第二次尝试那样继续:

local_time = timezone.localtime(timezone.now()) 
mytime = roundTime(local_time, timedelta(minutes=15))

Answer 2

要舍入时区感知的datetime对象，将其设置为朴素datetime对象，将其舍入，并为舍入时间附加正确的时区信息:

from datetime import timedelta
from django.utils import timezone
def round_time(dt=None, delta=timedelta(minutes=1)):
    if dt is None:
        dt = timezone.localtime(timezone.now()) # assume USE_TZ=True
    tzinfo, is_dst = dt.tzinfo, bool(dt.dst())
    dt = dt.replace(tzinfo=None)
    f = delta.total_seconds()
    rounded_ordinal_seconds = f * round((dt - dt.min).total_seconds() / f)
    rounded_dt = dt.min + timedelta(seconds=rounded_ordinal_seconds)
    localize = getattr(tzinfo, 'localize', None)
    if localize:
        rounded_dt = localize(rounded_dt, is_dst=is_dst)
    else:
        rounded_dt = rounded_dt.replace(tzinfo=tzinfo)
    return rounded_dt

为了避免浮点问题，所有的计算都可以用整数微秒(dt.resolution)来重写。

的例子:

>>> round_time(delta=timedelta(minutes=15))