On 02/11/2010 16:23, Terry Reedy wrote:
On 11/2/2010 10:05 AM, C. Titus Brown wrote:
...but, as someone who has to figure out how to teach stuff to CSE
undergrads
(and biology grads) I hate the statement "...any programmer should
expect this..."
And indeed I (intentionally) did not say that. People who are ignorant
and inexperienced about something should avoid making expectations in
any direction until they have read the doc and experimented a bit.
Expectations come from consistent behaviour. sorted behaves consistently
for *most* of the built-in types and will also work for custom types
that provide a 'standard' (total ordering) implementation of __lt__.
It is very easy to *not realise* that a consequence of sets (and
frozensets) providing partial ordering through operator overloading is
that sorting is undefined for them. Particularly as it still works for
other mutable collections. Worth being aware that custom implementations
of standard operators will break expectations of users who aren't
intimately aware of the problem domains that the specific type may be
created for.
All the best,
Michael Foord
What I did say in the post you responded to is "Any programmer who
sorts (or uses functions that depend on proper sorting) should know
and respect the difference between partial orders, such as set
inclusion, and total orders, such as lex order of sequences." I should
hope that you teach the difference, or rather, help students to notice
what they already know. Tell them to consider that difference between
sorting people by a totally ordered characteristic like height or
weight and a characteristic that is at best partially ordered, like
hair color or ethical character. Or have them consider the partial
order dependencies between morning get-ready-for-class activities
(socks before shoes versus pants and shirt in either order). They
already do topological sorting every day, even if the name seems fancy.
--
http://www.voidspace.org.uk/
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