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Fri May 21 11:02:52 EDT 2004 · https://mail.python.org/pipermail/python-dev/2004-May/044929.html

On Thu, May 20, 2004 at 01:31:09PM -0400, Mark.Lake at aigfpc.com wrote:
[...]
> 
>    2. Sets are a useful addition to the language, but sorted sets (and
>    dictionaries) would be more useful.  C++/Java/C# all provide these types.
>    In particular I'd like to see:
> 
>    A.  Dictionaries support union, intersection, and symmetric difference
>    operations as sets do.

What's the intersection of {'a': 1} and {'a': 2}?  {'a': (1, 2)}?  What
about of {1.0: 'one point oh'} and {1: 'one'}?

Also, this would place a significant burden on people trying to implement
their own classes that present a dictionary-like interface, although perhaps
UserDict.DictMixin could help there...

A PEP for this that's more than a sentence long would probably be a good
idea :)

[...]
>    C. Binary searching for items in sorted sequence and mapping types.

See the bisect module.  I'm not sure what binary searching of a mapping type
would mean, though (I guess you mean for your proposed sorted dictionary
type?).

>    D. Ability to handle multiple getitems at once in sequence and mapping
>    types (Akin to what can be done in numarray).  Certainly there is no good
>    reason why lists/tuples shouldn't support list[iterable] (not to be
>    confused with list(iterable)) which returns or dictionaries support
>    something like dict.getm(iterable).

Well, one reason is that it places a greater burden on people implementing
__getitem__, and it doesn't really offer much improvement over:
    [l[x] for x in iterable]

Or for dictionaries:
    dict(d[x] for x in iterable)  # Assuming 2.4's generator expressions.

-Andrew.

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[Python-Dev] sets, scanf