Re: Why does TimestampFromMx chop off the milliseconds?

Hi all,

I know it's bad form to respond to yourself, but I figured out why 
psycopg.TimestampFromMX() chops off the fractional seconds.  Internally 
the strftime method of mx.DateTime objects is used, and the strftime 
function has no way to specify fractional seconds in the output.  
Additionally, the struct tm data type only uses an integer number of 
seconds.

I was able to successfully use str() on my DateTime objects to get a 
full timestamp like I wanted.

Now I am fighting a different battle.  Sometimes the original 
mx.DateTime object I inserted and the one retrieved from the database 
do not match.  I think that it probably has something to do with 
floating point rounding errors.

For example.

 >>> t1 = DateTime(2002,12,4,14,27,2.170)
 >>> str(t1)
'2002-12-02 16:27:02.16'
 >>> t1.absvalues()
(731186, 59222.169999999998)
 >>> 2+170/1000.0     # Which is how I calculate seconds for the 
DateTime constructor
2.1699999999999999

I think that the problem is that str() on a DateTime object truncates 
the seconds value at 2 digits, and there's no way I've fond to get it 
to give more precision or round correctly.  O suppose that I could make 
my own version of strftime that does what I want in python.  Gah.

Cheers,
	Chris

On Wednesday, December 4, 2002, at 01:38 PM, Chris Douty wrote:

> Why, oh why, do the various Time* functions in psycopg ignore 
> fractional seconds?
>
> I really need to preserve fractional seconds.  I just noticed that all 
> of my timestamps were truncated by psycopg.  I can see two potential 
> workarounds, use the str() function on my mx.DateTime object and 
> insert the string.  The other option is to fix the source to psycopg 
> so that these functions don't truncate my timestamps.  I guess that's 
> not really a workaround, that open source. 
>
> What really has me perplexed is that psycopg properly retains the 
> fractional seconds when converting
> a database timestamp field into a mx.DateTime object.  WTF?

--

-- 
Christopher Douty <Chris_Douty@...> +1-650-367-3129
Senior Engineer, Software & Systems  - AMPEX Data Systems Corp.