.dbf tables and Null

John Machin sjmachin at lexicon.net
Sat Aug 1 04:41:30 CEST 2009


On Aug 1, 3:41 am, Ethan Furman <et... at stoneleaf.us> wrote:
> Mornin'!  and a good one, too, I hope.
>
> Question for you...
>
> First part of the question:  What is the general value in having Null
> capability for fields?

In general, in any database system, so that one can distinguish
between "the customer has no 'middle name'" ('') and "the customer's
'middle name' is unknown" (NULL).

>
> Second part:  Is there a tangible difference between Null, and the
> nothing of 0, '', False, etc, in python?

0 is the zero thing, it is not nothing. False is not nothing.


>
> Third part:  If there is a tangible difference, do those of us who use
> python and these old, refuse-to-die, .dbf files actually have need of,
> or have tables including, Null values?
>
> P.S. part (for John Machin, if he sees this  ;)
> Will the dbf package you are working on support Null values?

My philosophy when digging stuff out of arcane storages is to expose
what is found and leave any kludging/sanitising to the next layer.

For example, None is returned for an N (Number) field that's all
spaces; it's up to the caller to decide whether to treat None as zero,
raise an exception, pop up a data-collection dialogue box, ...

If you mean specifically the Visual Foxpro v3 _NullFlags hack, yes, it
already supports that, as well as the VFP9 abuse of that hack for
Varchar and Varbinary fields :-)



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