Hi all I've recently been writing some code that for various reasons needs to support a couple of different PostgreSQL APIs for Python, and have the potential for MySQL support down the track. I've been running into a fair bit of trouble with the DB API, in particular the freedom it gives DB module implementers with regards to Cursor.execute() argument formatting.
http://python.org/peps/pep-0249.html says that DB modules must have an attribute paramstyle, to tell the code using the module what string format convention it requires: paramstyle String constant stating the type of parameter marker formatting expected by the interface. Possible values are [2]: There is no discussion, however, of why these _five_ different format styles are permitted, nor any way the calling code might compensate for this. Some APIs seem to support more than one style (PyPgSQL comes to mind here, with both printf+arglist and extended printf+dict support), but there is no apparent way to discover this. Some modules support changing paramstyle, others do not, and there's no spec coverage for this. This seems to my eyes like a fairly major DB API wart, assuming there's no nice way to get around it that I'm not aware of. Do I need to write a format_for_db_API(dbiapi.paramstyle,formatstring) function that converts an extended printf string to whatever the DB API expects, then use that every time I call Cursor.execute() ? If so, is there any chance of the eventual release of a DB API 2.1 that provides a single calling convention that MUST be supported? Any enlightenment on this would be much appreciated. I've found the Python DB API very nice to work with so far (my previous generalised DB API experience being with the DBI:: package in Perl) but this is really frustrating me. If worst comes to worst, I'll just write a simple cursor wrapper that can translate extended printf calls to whatever the DB API requires, but it'd be much nicer not to have to implement something as ugly as that to work around an issue with an otherwise very nice and clear API. Some digging around on Google Groups suggests that others have run into this problem, and quite a few have grumbled about it, but there have been no real answers. So: Would there be any interest in releasing a DB-API 2.1 with one parameter style made MANDATORY, and a tuple of other supported styles in .paramstyles ? I think existing modules implemented in Python could be retrofitted to take extended printf quite easily, though at a small performance cost when extended printf was used. Modules in pure C would be more work, but still probably not a big deal. -- Craig Ringer -- http://mail.python.org/mailman/listinfo/python-list
