[Python-ideas] Putting `blist` into collections module

[Nick Coghlan]

On 21 September 2014 15:18, David Wilson <dw+python-ideas at hmmz.org> wrote:
>
> Even after reviewing the original PEP, the presence of OrderedDict (and
> particularly under that moniker) feels wrong. Since its addition, in
> every case I've encountered it in commercial code, the use has been
> superfluous, diabolically miscomprehended, or used as a hacky stand-in
> for some cleaner, simpler approach.

The main intended use case for OrderedDict was preserving insertion
order, such as when executing code, parsing a JSON file, or
maintaining an LRU cache.

For many cases involving a *sorted* key, just sorting when necessary
is often easier than preserving sort order on every update (not
necessarily *faster*, but often fast enough that the extra dependency
isn't justified).

That's the background any proposal needs to compete against:
OrderedDict covers preserving insertion order, while actually sorting
the keys or items when the sorted order is needed covers the sorting
case.

The needle to be threaded to get a "sorted container" into the
standard library is clearly explaining *in terms a relatively junior
programmer can understand* when you would use it over dict or
OrderedDict. In particular, it likely needs to explain the trade-offs
between maintaining sort order on insert, and using an unordered
container that is sorted for display or serialisation.

That justification needs to be in the PEP to justify the initial
inclusion, but also in the eventual docs to help folks know when their
current problem is the "it" in There Should Be One Obvious Way To Do
It for the new type.

Regards,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia