sliciing dicts (was RE: More random python observations from a perl programmer)

[Tim Peters]

[tchrist]
>> GOTCHA: (medium)
>>     Slices in Python must be contiguous ranges of a sequence.
>>     In Perl, there's no such restriction.

[Michael Hudson]
> At some point Python will probably support `extended slice syntax'
> like so:
>
> range(0,10)[1:4:2] => [1,3]
>
> Numerical Python already does this.

[tchrist]
>> GOTCHA: (medium)
>>     You can't slice dictionaries at all in Python.  In Perl, it's
>>     easy to slice a hash, and just as sensible.

[Michael Hudson]
> Huh? What would that mean? There's no reason to suspect that the keys
> of a dictionary are ordered.

What Tom calls "slicing" here the NumPy folk would call gather/scatter
subscripting.  A list can be used as an index, e.g.

    thing[[7,2,3]] == [thing[7], thing[2], thing[3]]

Perl has something like that; Python does not.

can't-tell-the-subscripting-modes-without-a-scorecard-ly y'rs  - tim