[Python-3000] dbm package creation

[Georg Brandl]

Guido van Rossum schrieb:

>>>>> Or is there an expected future use case where the returned value would
>>>>> be something in a *different* package?
>>>>
>>>> There was in the past, with the now-defunct bsddb185 module which was
>>>> not used by anydbm.
>>>>
>>>>> Returning a module object would seem the least attractive version --
>>>>> that would require importing the module, which may not be in the
>>>>> caller's plan at all.
>>>>
>>>> It may not be, but the modules are imported anyway during import of
>>>> dbm.__init__ (which contains whichdb() now.)
>>>
>>> Hm, that's a regression if you ask me. Couldn't you use lazy import?
>>
>> There's a module attribute "error" -- supposed to be a tuple of all
>> possible errors from the db modules; that is hard to make lazy.
>>
>> Of course we could solve this by making all the different db module
>> errors subclasses of a common exception (but since most of them are
>> defined in C modules, this is hard again.)
> 
> OK, let's make the latter a stretch goal. :-)

I just realized: since dumbdbm's "error" is just IOError, using
"except [any]dbm.error" will always catch IOError.

So the easy solution is to just derive the database error classes
from IOError.

The slightly harder solution is to declare the above a bug, create
a new builtin (at least on C level) error class DBError and derive
them from that.

Georg