DateTime::Format::Strptime Parsing Seems to have a Problem?

ozboomer has asked for the wisdom of the Perl Monks concerning the following question:

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Re: DateTime::Format::Strptime Parsing Seems to have a Problem?
by tangent (Vicar) on Mar 26, 2019 at 03:09 UTC

%I

%H

pattern => '%d/%m/%Y %I:%M:%S %p'
[download]

%r

pattern => '%d/%m/%Y %r'
[download]

[reply]
[d/l]
[select]

Re: DateTime::Format::Strptime Parsing Seems to have a Problem?
by Athanasius (Bishop) on Mar 26, 2019 at 03:20 UTC

Hello ozboomer,

tangent beat me to it with %I. But you should also check for errors; e.g.:

my $dmy_fmt = DateTime::Format::Strptime->new
   (
       pattern   => '%d/%m/%Y %I:%M:%S %p',
       time_zone => 'Australia/Victoria',
       on_error  => 'croak',    # <-- ADD THIS
   );
[download]

With %H instead of %I, this reports:

13:08 >perl 1989_SoPW.pl
$dtnow: !2019-03-25T20:10:32!
 $lodt: !2019-03-18T10:12:53!
Parsed an input with 24-hour and AM/PM values that do not match - "3" 
+versus "pm" at 1989_SoPW.pl line 48.

13:10 >
[download]

— somewhat cryptic, but an indication that DateTime::Format::Strptime is expecting 24-hour and not 12-hour time here.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re: DateTime::Format::Strptime Parsing Seems to have a Problem?
by ozboomer (Friar) on Mar 26, 2019 at 04:23 UTC

Appreciate the info... Seems I "couldn't see the forest for the trees" or something, as I was looking for the "12-hour" formatter... but didn't "see" the "%I"...(!)

The final part of the puzzle is to understand how to ensure we can set-up a sequence of datetimes that are 1 day apart. If the mentioned mods are made to the code... and I add some additional code for setting-up a Recurrence, the code becomes:-

use strict;
use warnings;
#use diagnostics;

use DateTime;
use DateTime::Format::Strptime;
use DateTime::Event::Recurrence;  # PART 2

our $LocalTZ = DateTime::TimeZone->new( name => 'local' );

my $dtnow = DateTime->now(time_zone => $LocalTZ);    # Current *local*
+ time
printf("\$dtnow: !%s!\n\n", $dtnow);

my $lo = "18/03/2019 10:12:53 am";     # Always works
my $hi = "24/03/2019 3:15:00 pm";      # Does not work... the format I
+ need to use
# my $hi = "24/03/2019 03:15:00 pm";     # Does not work
# my $hi = "24/03/2019  3:15:00 pm";     # Does not work
# my $hi = "24/03/2019 15:15:00 pm";     # Works but 15hrs with 'pm' i
+s silly
# my $hi = "24/03/2019 15:15:00";        # Works 

my $dmy_fmt = DateTime::Format::Strptime->new(  # Let DateTime use 'dd
+/mm/yyyy'
        pattern   => '%d/%m/%Y %I:%M:%S %p',
#        pattern   => '%d/%m/%Y %I:%M:%S',  # Use this when no 'am/pm'
+ in the date string
#        time_zone => 'Australia/Victoria',
        time_zone => 'local',
        on_error  => 'croak'
    );
   
my $lodt = $dmy_fmt->parse_datetime($lo);    
printf(" \$lodt: !%s!\n", $lodt);
   
my $hidt = $dmy_fmt->parse_datetime($hi);    
printf(" \$hidt: !%s!\n", $hidt);

# ========== PART 2 ==========

my $rec1  = DateTime::Event::Recurrence->daily(start => $lodt);
# $rec1->set_time_zone('local'); # Doesn't change the 'mis-conversion'
my @days = $rec1->as_list( start => $lodt, end => $hidt );

printf("1st Format DAYS:\n");
foreach my $day (@days) {
   printf("  %s\n", $day->dmy("-"));
}
printf("\n");

# ---- A different (truncated) format

my $strp = DateTime::Format::Strptime->new(
    pattern   => '%d/%m/%Y',
    time_zone => 'local',
    on_error => 'croak'
);

my $dt1 = $strp->parse_datetime("18/03/2019");
#my $dt1 = $strp->parse_datetime($lo);
printf("  \$dt1: !%s!\n", $dt1);

my $dt2 = $strp->parse_datetime("24/03/2019");
#my $dt2 = $strp->parse_datetime($hi);
printf("  \$dt2: !%s!\n", $dt2);

my $rec2 = DateTime::Event::Recurrence->daily(start => $dt1);
@days = $rec2->as_list( start => $dt1, end => $dt2 );
printf("2nd Format DAYS:\n");
foreach my $day (@days) {
   printf("  %s\n", $day->dmy("-"));
}
printf("\n");
[download]

Here, the output is:-

$dtnow: !2019-03-26T15:05:02!

 $lodt: !2019-03-18T10:12:53!
 $hidt: !2019-03-24T15:15:00!
1st Format DAYS:
  19-03-2019
  20-03-2019
  21-03-2019
  22-03-2019
  23-03-2019
  24-03-2019

  $dt1: !2019-03-18T00:00:00!
  $dt2: !2019-03-24T00:00:00!
2nd Format DAYS:
  18-03-2019
  19-03-2019
  20-03-2019
  21-03-2019
  22-03-2019
  23-03-2019
  24-03-2019
[download]

So, it seems DateTime::Format::Strptime is looking at the input strings (which are local times) and converting them according to the 'time_zone' item (which is 'local')... and thus, the resultant objects contain the same time field values.

However, when the recurrence is set-up for the "dd/mm/yyyy hh:mm:ss p"-derived objects, the date is incorrect. I thought it might have to do with the time zone... but setting the time zone on the occurrence made no difference to the dates it came up with.

More confusing, if I set-up a recurrence using the "dd/mm/yyyy"-derived objects, the date is correct, although the time of day is set to 00:00:00 (obviously and reasonably).

So, how does the recurrence using "dd/mm/yyyy hh:mm:ss p"-derived objects need to be configured to display the correct dates, including time of day?