Re: flexi adaption/casting scheme

Hi Daniele,

> For example, to cast composite to dictionaries one can subclass it as:
>
> class DictComposite(psycopg2.extras.CompositeCaster):
> def make(self, attrs):
> return dict(zip(self.attnames, attrs))
>

This is nifty! I can then just slightly adjust above to filter for attrs
which are not None (only include those into the dict).

> Tobias: as expected it works ok with composite types, as the original
> CompositeCaster does:
>
> # from psql: CREATE TYPE card_back AS (face card, back text);
>
> c2 = DictComposite.from_db('card_back', cnn)
> c2.register()
>
> cur.execute("select ((8, 'hearts'), 'blue')::card_back")
> cur.fetchone()[0]
> {'back': 'blue', 'face': {'suit': 'hearts', 'value': 8}}
>
> if it doesn't work for you, you are probably doing something wrong.

I am struggling with _adaption_ (Python dict => PG composite), not
_typecasting_ (PG composite => dict).

My understanding would be that the following code should work with an
unmodified Psycopg, but it does not:

https://github.com/oberstet/scratchbox/blob/master/python/psycopg2/test7.py

What am I doing wrong?

Thanks!
Tobias