Open Stack

Thanks Yunhong for pointing this issue out and submitting a patch
in quick order.

Your reasoning for switching from if offset to if offset is None,
in order to avoid including the offset==0 case, makes perfect sense.

You'll just have to propose the change first to openstack-common,
from where it will be copied to the nova, glance etc. codebases.

Cheers,
Eoghan 


----- Original Message -----
> I create a patch for it https://review.openstack.org/#/c/12705/ and
> please help to review.
> 
> Thanks
> --jyh
> 
> > -----Original Message-----
> > From: openstack-bounces+yunhong.jiang=intel.com at lists.launchpad.net
> > [mailto:openstack-bounces+yunhong.jiang=intel.com at lists.launchpad.net]
> > On
> > Behalf Of Jiang, Yunhong
> > Sent: Monday, September 10, 2012 8:17 AM
> > To: Robert Collins
> > Cc: openstack at lists.launchpad.net
> > Subject: Re: [Openstack] One potential issue on the
> > normalize_time() in
> > timeutils
> > 
> > Rob, thanks for comments.
> > I totally agree with you that aware datetime object is better than
> > naive one.
> > The key thing is, utcnow() will return naive object, that means in
> > some time, we
> > have to use naive object to compare with utcnow(), and we need a
> > conversion
> > function to convert from aware to naive. The normalize_time() is
> > the best
> > candidate for this purpose, but it will fail to convert to naive
> > datetime object in
> > some situation. That's why I send the mail. I just want to change
> > the
> > normalize_time() to make sure it will always return naive object.
> > 
> > Thanks
> > --jyh
> > 
> > > -----Original Message-----
> > > From: Robert Collins [mailto:robertc at robertcollins.net]
> > > Sent: Monday, September 10, 2012 3:25 AM
> > > To: Jiang, Yunhong
> > > Cc: eglynn at redhat.com; openstack at lists.launchpad.net
> > > Subject: Re: [Openstack] One potential issue on the
> > > normalize_time()
> > > in timeutils
> > >
> > > On Mon, Sep 10, 2012 at 3:09 AM, Jiang, Yunhong
> > > <yunhong.jiang at intel.com>
> > > wrote:
> > > > Hi, Eoghan and all,
> > > >
> > > >         When I implement an enhancement to trusted_filter, I
> > > >         need
> > > > utilize
> > > timeutils() to parse ISO time. However, I suspect there is one
> > > potential issue in
> > > normalize_time() and want to get some input from your side.
> > > >
> > > >         In normalize_time(), if the parameter "timestamp" is an
> > > > aware
> > > object (http://docs.python.org/library/datetime.html) , it's
> > > output
> > > will vary depends on the input. If the timestamp is UTC time, it
> > > will
> > > be return as is without convention, i.e still an aware object.
> > > However, if it's not an UTC time, it will be converted to be a
> > > naive object.
> > > >         This mean that the function will return different type
> > > > depends on
> > > input, that's not so good IMHO.
> > > >
> > > >         The worse is, any compare/substract between naïve
> > > >         object and
> > > > aware object will fail. Because the timeutils.utcnow() and
> > > > datetime.datetime.now() returns naive object, so
> > > > compare/substract
> > > > between the uctnow() and normalize_time() may fail, or not,
> > > > depends
> > > > on input from the API user. I'm a bit surprised that
> > > > changes-since
> > > > works on such situation :)
> > > >
> > > >         I suspect this is caused by the "if offset". When
> > > >         timestamp
> > > > is
> > > naïve object, the offset is None. Thus check "if offset" will
> > > avoid
> > > operation type exception. However, if the timestamp is UTC time,
> > > the
> > > offset will be date.timeslot(0), which will return false also for
> > > "if offset".
> > > >
> > > >         Are there any special reason that we need keep aware
> > > >         object
> > > > if
> > > input is at UTC time already? Can I changes the function to
> > > always
> > > return naive object? If yes, I can create a patch for it.
> > >
> > > You are probably better off creating an aware datetime object,
> > > and
> > > using them pervasively across the codebase, than using naive
> > > objects.
> > > As you note, they are not interoperable, and I've seen countless
> > > bugs
> > > where folk try to mix and match. If we want to show local date
> > > time to
> > > users *anywhere*, we'll need TZ aware objects, which is why that
> > > variation is the one to standardise on. Otherwise, you end up
> > > with
> > > multiple conversion points, and you can guarantee that at least
> > > one will get it
> > wrong.
> > >
> > > -Rob
> > 
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