Re: Determining next DST transition
On 30/07/2010 14:59, Anthony R. J. Ball wrote: On Fri, Jul 23, 2010 at 04:39:58PM +0100, Elliot Merrony wrote: Hi all I filed this bug last week and Dave Rolsky advised me to post here to explain what I was trying to do: I created a simple lib to do this, though it really should be made available in the main libs. It takes a year or range of years and looks at the internals to find the DST transitions for the years in question. Here it is. (tried to send when you first posted, but I'm having mail server issues) [code] Many thanks for this Anthony, will give it a go. And apologies for time taken to respond, I also have mail/news/connection issues... Elliot
Re: Determining next DST transition
On Fri, Jul 23, 2010 at 04:39:58PM +0100, Elliot Merrony wrote:
Hi all
I filed this bug last week and Dave Rolsky advised me to post here
to explain what I was trying to do:
I created a simple lib to do this, though it really should be made available in
the main libs. It takes a year or range of years and looks at the internals to
find the DST transitions for the years in question.
Here it is. (tried to send when you first posted, but I'm having mail server
issues)
#!perl
package TZInfo;
use strict;
use DateTime;
use POSIX;
use constant UTC_START = 0;
use constant UTC_END = 1;
use constant LOCAL_START = 2;
use constant LOCAL_END = 3;
use constant OFFSET = 4;
use constant IS_DST = 5;
use constant SHORT_NAME = 6;
sub get_dst_lib_info {
{ version = DateTime::TimeZone::Catalog::Olson Version(),
last_updated = ( stat( $INC{'DateTime/TimeZone/Catalog.pm'} ) )[9]
};
}
# call with year or array ref of two years for range and timezone to check.
sub get_dst_changes {
my $year = shift;
my $tz = shift;
my ($DT,$DT_end);
if(ref $year eq 'ARRAY') {
eval { $DT = DateTime-new( %{$year-[0]}, time_zone = $tz ) };
return if $@;
eval { $DT_end = DateTime-new( %{$year-[1]}, time_zone = $tz ) };
return if $@;
} else {
eval { $DT = DateTime-new( year = $year, time_zone = $tz ); };
return if $@;
$DT_end = $DT-clone();
$DT_end-add( years = 1 );
}
my $i = 100;
my @out;
while ( $i-- ) {#in case we start looping for some reason
my $span = $DT-{tz}-_span_for_datetime( 'utc', $DT );
my $seconds = $DT-utc_rd_as_seconds();
#if($span-
if($span-[UTC_END] =~ /\+/) {
last;
}
my $change = $span-[UTC_END] - $seconds;
# Find the offset and add it. Now we have a DateTime object AT DST
change
$DT-add( seconds = $change );
my $DT2 = $DT-clone();
$DT-add( seconds = 1 );# One second past allows us to search for
the next DST change
last unless $DT $DT_end;
push @out, $DT2;
}
\...@out;
}
1;
Re: Determining next DST transition
On Fri, 23 Jul 2010, Elliot Merrony wrote: To start from the beginning, I've been using the DT and DT:TZ modules for a world clock and want to add a feature which displays the time, date and effect of the next DST transition (if any) for each location. The modules seem to allow me to do anything I could possibly imagine with times and time zones, except this. I realise I could test whether each location is on DST for every hour from now until 6 months ahead, but was hoping that there was a more elegant way of determining when the transition is. Asking around, I was advised that the _rules attribute of an DateTime::TimeZone object returns an array of DateTime::TimeZone::OlsonDB::Rule objects which encode the start and end of DST observances. However, I'm now understanding from Dave's response to the bug that the _rules attribute neither is nor should be used for this purpose. Any advice welcomed. Please bear in mind I'm a Perl beginner (I'm only using it due to the existence of these modules!) so apologies for any misunderstanding. Basically, I think we could have a better API than returning the raw rules. Off the top of my head, I think a DateTime::Event module that let you ask for the next transition in a set would work well. Of course, that might still require opening up some chunk of the DT::TimeZone API, but I don't want to expose the raw _rules attribute directly. -dave /* http://VegGuide.org http://blog.urth.org Your guide to all that's veg House Absolute(ly Pointless) */
