[web2py] Re: in a db query, why the error: can't compare datetime.datetime to Field

[Luis Goncalves]

Ah yes! Thank you, Greg!

I come from the Matlab world and am not very experienced with object 
oriented program, but I was suspecting it was something like that.

I think I found a true bug in the way datetime objects work in db queries, 
though -- I will post under a new subject heading.

Thanks!!!

Luis.

[web2py] Re: in a db query, why the error: can't compare datetime.datetime to Field

[Gregory Hellings]

If I understand what you're doing there it is a limitation of the
language.  db.entry.DT  my_DT works because Field has defined a
special language construct for when the datetime is compared to the
Field. However, my_DT  db.entry.DT does not work, because there you
are comparing a Field to a datetime.  Python (and C++, etc) allow you
to define a function to be called when your object is on the left side
of a comparison, but not if it is on the right (unless, of course, an
object of that class is on both sides of the operator).

This could be avoided if someone wanted to custom extend the datetime
object to define the comparison functions, but then a person would
have to use contrib.datetime instead of the built in datetime class.
It's just _The Way Things Are_ and is common for languages which allow
a custom override of comparison operators.

--Greg

On Aug 18, 6:43 pm, Luis Goncalves lgoncal...@gmail.com wrote:
 Let

 my_DT = datetime.datetime( 2011, 08, 16)

 db.define_table( 'entry', Field('DT' = 'datetime' ) )

 (and add data records to the database ...)

 In a db query, this works:

 db( db.entry.DT my_DT).select()

 but this does not:

 db( my_DT db.entry.DT).select()

 producing error :   can't compare datetime.datetime to Field

 Why does that happen?

 Thanks,
 Luis.