On 01.02.2015 22:47, Michael Bayer wrote: > Hi - > > May I get clarification from pep-249 regarding the contract for fetchall() > and fetchmany(), as to if it is acceptable and/or recommended that these > methods return tuples of tuples, as opposed to lists of tuples? > > In my experience, while tuples and lists are just “sequences” that are > immutable / mutable, there is a more subtle semantic distinction between > them, in that lists are for variable-length collections of homogenous > elements (e.g. rows), whereas tuples are appropriate for fixed-length > collections of heterogenous elements (e.g. column values). > > If this is the case, pep-249’s use of the language "e.g. a list of tuples” > leaves this open to interpretation and inconsistency, like so many other > things. I’d like to get some language, at least in email here, that lists > are recommended, if this is the case. Otherwise, I guess it’ll just be > another thing for me to suggest for DBAPI-3 :). > > thanks for your attention!
We have made this more general in the DB-API to allow authors to create e.g. result set objects which implement the sequence API and row objects which also implement sequence API. I know several database modules which provide ways to have the fetch methods return row objects, but I'm not aware of ones which implement a result set object. You get the best performance using lists of tuples. Tuple creation is fast and lists are ideal for variable length storage of objects. Using tuples for result sets is not a very useful thing to do, since you typically want to manipulate the result set in the application. -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Feb 02 2015) >>> Python Projects, Coaching and Consulting ... http://www.egenix.com/ >>> mxODBC Plone/Zope Database Adapter ... http://zope.egenix.com/ >>> mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/ ________________________________________________________________________ ::::: Try our 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 https://mail.python.org/mailman/listinfo/db-sig
