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Thursday, February 2, 2006

How to programatically convert stupid 12 hour timestamps to 24 hours

Every time I have to manually parse a 12 hour timestamp (with "am" and "pm") into a 24 hour format I have to think about it to get the logic right. Now I won't have to again:

def twelveto24(hr, per):

    if hr == 12 and per == 'a': return 0

    if hr != 12 and per == 'p': return hr+12

    return hr



hours = range(1,13)

hours = zip(hours,['a']*12)+zip(hours,['p']*12)



for hr, per in hours:

    print twelveto24(hr, per),



#results

1 2 3 4 5 6 7 8 9 10 11 0 13 14 15 16 17 18 19 20 21 22 23 12

Update: For the hell of it, here's the Perl code I wrote to do the thing I actually had to do:

sub getTimestamp{

    #02/01/2006,05:06:04am

    $_[0] =~ m@\[(\d+)/(\d+)/(\d+),(\d+):(\d+):(\d+)([aApP])[mM]\]@;

    return "$3-$1-$2 ".sprintf("%02d",twelveto24($4,lc($7))).":$5:$6";

}



sub twelveto24{

    ($hr, $per) = @_;

    return 0 if($hr == 12 and $per eq 'a');

    return $hr+12 if($hr != 12 and $per eq 'p');

    return $hr;

}



print getTimestamp("[02/01/2006,12:06:04am]");

#2006-02-01 00:06:04

Permalink | 7 Comments | Tags: Programming | id 7890

11:01 (utc-6)
edited: 18:06 (utc-6)

Comments

Will strtotime() work for this?

Yeah, it would. And it even worked fine on the date format I just had to parse:

$ php -r "echo date('c',strtotime('02/01/2006,12:06:04am'));"

2006-02-01T00:06:04-06:00

(hey, central time zone )

But, I was working in Perl, and there are no built-in date parsing libraries in Perl.

∴ Keith | 2-Feb-2006 3:08pm est | http://keithdevens.com/ | #9089

I couldn't find a strtotime() for Perl, but CPAN has Date::Manip and Time::Format that should do it (I think).

Yeah, CPAN has some things, but unfortunately there's nothing standard.

∴ Keith | 2-Feb-2006 7:54pm est | http://keithdevens.com/ | #9091

use Date::Parse qw/str2time/; for the next time that comes up ...

Of course, but like I said, there's nothing standard:

C:\temp>cat test.pl

use Date::Parse qw/str2time/;



print "hello";

C:\temp>test.pl

Can't locate Date/Parse.pm in @INC (@INC contains:

   C:/Perl/lib C:/Perl/site/lib .) at C:\temp\test.pl line 1.

BEGIN failed--compilation aborted at C:\temp\test.pl line 1.

(wrapped so it doesn't break my layout) BTW, I don't think I ever linked this article on handling dates and times with Perl, but I think that was one of the things I looked through. Point was, I couldn't go installing modules on the server I was working on.

∴ Keith | 5-Mar-2006 11:09am est | http://keithdevens.com/ | #9251

Ah, right. Yeah, Perl's a signficantly suckier language when you can't install modules; I wrote this earlier today, for example, and I'm not proud of it:

    # We need an actual file to pass to the openssl command-line

    # tool. Create it using the Perl temporary file module.

    my ($temp_file_handle, $temp_file_name)

        = tempfile DIR => $tempdir;



    # Flush writes to the file that we're going to hash

    # automatically.

    $| = 1, select $_ for select $temp_file_handle;



    # Write the secret prefix and the content to the file, so the hash

    # operation takes place on the same string on both ends

    print { $temp_file_handle } SIGNING_PREFIX.$content;

    close $temp_file_handle;

    my $hash = `/usr/bin/openssl dgst -sha1 < $temp_file_name`;

    unlink $temp_file_name;

∴ Aidan Kehoe | 5-Mar-2006 11:44am est | http://www.parhasard.net/ | #9256

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