[Tutor] Why is an OrderedDict not sliceable?

[Albert-Jan Roskam]

> To: tutor at python.org
> From: ben+python at benfinney.id.au
> Date: Fri, 22 Jan 2016 04:12:08 +1100
> Subject: Re: [Tutor] Why is an OrderedDict not sliceable?
> 
> Ben Finney <ben+python at benfinney.id.au> writes:
> 
> > Oscar Benjamin <oscar.j.benjamin at gmail.com> writes:
> >
> > > According to a narrow definition of indexed access. I would say that
> > > d[k] is index access even if d is a dict and k a key.
> 
> The sense of “index” implied is used consistently throughout Python
> <URL:https://docs.python.org/3/glossary.html> to refer to the integer
> ordinal position in a sequence.

I appear to have confused the terms "sorted" and "ordered" (see the email I just sent to Mark Lawrence).  My OrderedDict was sorted on its keys, because I defined the dict using the result of an SQL query that ended with ORDER BY <names of dict keys here>. So in that case I needed a kind of "chameleon" datatype: both a mapping and an indexing type [1]
[1] https://docs.python.org/2/reference/datamodel.html#object.__getitem__ 
 

> It is not compatible with key access into a mapping.
> 
> > An index implies the ordinal position in a sequence. In a mapping, the
> > key is *not* referring to the position in a sequence, so is not a key.
> 
> “the key … is not an index”, I mean.
> 
> > So accessing an item in a mapping by key is not indexed access.
> 
> -- 
>  \     “Facts do not cease to exist because they are ignored.” —Aldous |
>   `\                                                            Huxley |
> _o__)                                                                  |
> Ben Finney
> 
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