[python-sybase] NumericType not hashable?

[Dave Cole]

> By the looks of it, NumericType is not python hash table friendly.

It should be...  Can you tell us how you built the module and which
platform you are using?

This is what happens when I try using the hash functionality:

>>> import Sybase
>>> n = Sybase.numeric(2)
>>> type(n)
<type 'NumericType'>
>>> d = {n: 'two' }
>>> d[2] 
'two'
>>> m = Sybase.numeric(3L)
>>> d[m] = 'three'
>>> d[3]
'three'
>>> o = Sybase.numeric('4')
>>> d[o] = 'four'
>>> d[4]
'four'

With my new 0.35pre1 callback error handling I now have problems with
longs...

>>> m = Sybase.numeric(1231312313123133L)
>>> m
1231312313123133
>>> hash(m)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "Sybase.py", line 133, in _cslib_cb
    raise Error(_fmt_client(msg))
Sybase.Error: Layer: 2, Origin: 4
cs_convert: cslib user api layer: common library error: The conversion/operation resulted in overflow.

The numeric hash calculation tries to convert to an integer first in
order to work out an integer compatible hash.  So it looks like I am
going to have to create a fully internal CS_CONTEXT for doing things
which I know might fail - such as attempts to convert NumericType to
integer before doing a conversion to string then to long in order to
calculate the hash.

> That means that something like:
> 
> c.execute('select id, limit_id, name from Sublimit_cvt')
> rows = c.fetchall()
> for row in rows:
>     id, limit_id, name = row
> 
> c.execute('select id from MyTable')
> rows = c.fetchall()
> for row in rows:
>   id = row[0]
>   print map[id]
> 
> 
> will fail if id is of type AutomaticID in Sybase.
> 
> I'm not sure if this is required by DB API, but I think it violates
> the principle of least surprise.

can you try doing something like this:

c.execute('select id, limit_id, name from Sublimit_cvt')
rows = c.fetchall()
for row in rows:
    id, limit_id, name = row
    print id, type(id), hash(id)


> My workaround was to force a conversion to string, so my code now
> reads map[str(id)]. But maybe NumericType should be modified to act
> as any number when used as a hash key?  Any opinions?

It Already Does (TM) so I suspect there is something else going on,
maybe related to the compilation.

- Dave

-- 
http://www.object-craft.com.au