[Python-Dev] Cleaning-up the new unittest API (original) (raw)

Michael Foord fuzzyman at voidspace.org.uk
Tue Nov 2 17:29:36 CET 2010

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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