Help understanding the decisions *behind* python?

David Smith dns4 at
Tue Jul 21 11:14:37 EDT 2009

Piet van Oostrum wrote:
>>>>>> Hendrik van Rooyen <hendrik at> (HvR) wrote:
>> HvR> On Monday 20 July 2009 21:26:07 Phillip B Oldham wrote:
>>>> On Jul 20, 6:08 pm, Duncan Booth < at invalid.invalid> wrote:
>>>>> The main reason why you need both lists and tuples is that because a
>>>>> tuple of immutable objects is itself immutable you can use it as a
>>>>> dictionary key.
>>>> Really? That sounds interesting, although I can't think of any real-
>>>> world cases where you'd use something like that.
>> HvR> simplest is something like a point in the cartesian plane with
>> HvR> an associated attribute like colour.
> There are numerous other examples. Anytime you need a key that is not a
> single object but composed of more than one:
> Name + birthday
> Street + number + City
> Student + Course
> etc.

Compound keys (like what's listed above) can also be used for sorting
lists of dictionaries using DSU style sorting.  Something I believe (and
 I could be wrong) won't work with mutable types like lists.


More information about the Python-list mailing list