Message 110408 - Python tracker

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Author	belopolsky
Recipients	alexandre.vassalotti, belopolsky, eric.araujo, grubert, jackdied, rhettinger, schmir, zzzeek
Date	2010-07-16.00:57:02
SpamBayes Score	2.5841084e-06
Marked as misclassified	No
Message-id	<AANLkTinb5PYSr4vkO4heipkBYraXGkvE3PA73wS5440d@mail.gmail.com>
In-reply-to	<1279239999.22.0.237682571159.issue9269@psf.upfronthosting.co.za>

Content
On Thu, Jul 15, 2010 at 8:26 PM, mike bayer <report@bugs.python.org> wrote: .. > where is it defined that sets are not "supposed" to contain mutable items? such a requirement vastly limits the usefulness of sets. > Well, there is no such requirement. The actual requirement is that they should be hashable. For built-in types, however hashable is the same as immutable. Arguably, user-defined classes should emulate that. > Consider that relational database rows are mutable. A result set containing multiple rows which each have a primary key comprises a set, hashed on primary key. But other attributes of each row can be updated. Surely this is not controversial ? What Python data structure should I (and a whole bunch of Python ORMs) be using to represent mutable, relational database rows, unordered and unique on primary key, in memory ? Why wouldn't you represent a result set as a dict mapping primary key (tuple) to list of column values?

On Thu, Jul 15, 2010 at 8:26 PM, mike bayer <report@bugs.python.org> wrote:
..
> where is it defined that sets are not "supposed" to contain mutable items?   such a requirement vastly limits the usefulness of sets.
>

Well, there is no such requirement. The actual requirement is that
they should be hashable.  For built-in types, however hashable is the
same as immutable.  Arguably, user-defined classes should emulate
that.

> Consider that relational database rows are mutable.  A result set containing multiple rows which each have a primary key comprises a set, hashed on primary key.  But other attributes of each row can be updated.   Surely this is not controversial ?  What Python data structure should I (and a whole bunch of Python ORMs) be using to represent mutable, relational database rows, unordered and unique on primary key, in memory ?

Why wouldn't you represent a result set as a dict mapping primary key
(tuple) to list of column values?

History
Date	User	Action	Args
2010-07-16 00:57:04	belopolsky	set	recipients: + belopolsky, rhettinger, grubert, jackdied, alexandre.vassalotti, schmir, eric.araujo, zzzeek
2010-07-16 00:57:03	belopolsky	link	issue9269 messages
2010-07-16 00:57:02	belopolsky	create