Caught out by daylight saving :-(
davea at dejaviewphoto.com
Mon Mar 30 14:56:10 CEST 2009
There isn't any right answer. There are two very different ways you can
interpret daylight savings time on a time conversion. I suspect you're
on Windows, trying to look at an old file's datestamp, and expect it to
look like Windows displays it. But Windows isn't even consistent with
itself, doing something different on a FAT system than on NTFS.
For most of my own purposes, I've decided to only store the UTC times
for things. Local time is useful only for interactive display. And
that interactive display is calculated according to some context.
To illustrate the problem, suppose you were in Chicago last month, and
modified a file at 2:00 pm, CST. And now you are located in PDT time
zone, and want to know when the file was last modified. Should you
convert the time zone and daylight savings, or should you convert only
time zone, or should you display the time as it was known to you at the
And to make it more complex, suppose the disk drive involved was located
in France. Just what time is correct?
Anything other than UTC is subject to confusion.
> Hi All,
> I had the following bit of code which was working fine until we went
> into Daylight saving this weekend, now the result is an hour out.
> timeString = "20090330 15:45:23"
> timeFormat = '%Y-%m-%d %H:%M:%S'
> modificationTime = datetime.datetime.utcfromtimestamp( time.mktime
> ( time.strptime( timeString, timeFormat ) ) )
> minutesToAdvance = datetime.timedelta( minutes=5 )
> modificationTime = modificationTime + minutesToAdvance
> datetimeString = str ( modificationTime ).replace( ' ', 'T' )
> The expected result should be:
> datetimeString = "20090330T15:50:23"
> But instead I get:
> datetimeString = "20090330T14:50:23"
> I believe it is going wrong at either the mktime() or utcfromtimestamp
> () stage.
> What is the correct way to fix this compensating for daylight saving
> SHaun >8)
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