Daniele Varrazzo wrote: >> On Jul 19, 2011 3:44 AM, "Federico Di Gregorio" >> <federico.digrego...@dndg.it> wrote: >>> At least 2 drivers (psycopg and pysqlite) provide a Python->backend >>> mechanism based on PEP 246, "Object Adaptation". If other implementors >>> are interested I can write a short explanation about how it works and >>> why it was chosen only for the Python->backend path and not for the >>> reverse. > > On Tue, Jul 19, 2011 at 11:05 AM, Vernon Cole <vernondc...@gmail.com> wrote: >> Yes, please. I would like to see that. Adodbapi has an output conversion >> mechanism, but I don't like it particularly well. > > For a description: > > http://initd.org/psycopg/docs/advanced.html#adapting-new-python-types-to-sql-syntax > http://initd.org/psycopg/docs/advanced.html#type-casting-of-sql-types-into-python-objects
While this is a nice system, it's also very slow. It uses function calls and string parsing/conversion for adapting each value. This works if you only have to insert/fetch a few rows, but won't be feasible for larger volumes. I think we need something more low-level, which tries to avoid (Python) function calls if possible, e.g. it should be possible to write adapters in C and only point to them using a symbol (sketching here): cursor.setinputconverter(BINARY, module.BINARY_INPUT_CONVERTER) cursor.setoutputconverter(BINARY, module.BINARY_OUTPUT_CONVERTER) For mxODBC we'd then use something like this: # Convert Python unicode object data to SQLWCHAR data cursor.setinputconverter(unicode, module.SQLWCHAR_INPUT_CONVERTER) # Convert SQL_WCHAR type code data to Python unicode cursor.setoutputconverter(SQL.WCHAR, module.SQLCHAR_OUTPUT_CONVERTER_UNICODE) The advantage here is that the database module could work directly on the internal data structure to implement the conversion rather than having to round-trip to Python. In order to provide the psycopg style adaption mechanism, the converter functions would have to be registered with converter codes, e.g. module.registerinputconverter(module.POINT_INPUT_CONVERTER, adapt_point) module.registeroutputconverter(module.POINT_OUTPUT_CONVERTER, cast_point) Lookup would then be a simple dictionary lookup on output (via the column type code) and a dictionary lookup/isinstance() loop for input mappings. -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Jul 19 2011) >>> Python/Zope Consulting and Support ... http://www.egenix.com/ >>> mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/ >>> mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/ ________________________________________________________________________ ::: Try our new mxODBC.Connect Python Database Interface for free ! :::: eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/ _______________________________________________ DB-SIG maillist - DB-SIG@python.org http://mail.python.org/mailman/listinfo/db-sig
