[Dev] blog post on why date math is *fun* (unless your a PHP coder)

[Grant Baillie]

On Nov 3, 2005, at 10:39, Phillip J. Eby wrote:

> At 01:27 AM 11/3/2005 -0500, Mike Taylor wrote:
>> Just thought I would share the blog post with other devs -  
>> something to always keep in the back of your brain when  
>> manipulating dates :)
>>
>> http://www.alexking.org/blog/2005/11/02/nasty-php-oddity/
>
> FWIW, in Python you should use a timedelta(days=whatever) to move  
> by days.  That's why timedelta keeps the days separate from the  
> seconds and such.  (That is, because there are days that aren't  
> 86400 seconds long.)

More generally, doing arithmetic directly on datetime fields (as  
opposed to using timedelta) is usually a bad idea. For example, see

<https://bugzilla.osafoundation.org/show_bug.cgi?id=4367>

--Grant