[Python-ideas] ordered dict

[Terry Reedy]

"BJörn Lindqvist" <bjourne at gmail.com> wrote 
in message 
news:740c3aec0704202128g6537c5bfv94c0f60a5d883d76 at mail.gmail.com...
>On 4/20/07, Terry Reedy <tjreedy at udel.edu> wrote:
>> 2. Order in the sorting or collation sense, which I presume you mean. 
>> To
>> reduce confusion, call this a sorted dictionary, as others have done.

>> Regardless, this has the problem that potential keys are not always 
>> comparable.

Current example:
>>> [1, 1j].sort()

Traceback (most recent call last):
  File "<pyshell#2>", line 1, in -toplevel-
    [1, 1j].sort()
TypeError: no ordering relation is defined for complex numbers

>>  This will become worse when most cross-type comparisons are
>> disallowed in 3.0.

> >>> l = [(), "moo", 123, []]
> >>> l.sort()
> >>> l
> [123, [], 'moo', ()]

Py 3.0 will raise an exception here as these will all be incomparable.

> If it is not a problem for lists it is not a problem for ordered 
> dictionaries.

But it *is* currently a problem for lists that will become much more 
extensive in the future, so it *is* currently a problem for sorted dicts 
that will be much more of a problem in the future.  Hence, sorted dicts 
will have to be restricted to one type or one group of truly comparable 
types.

Terry Jan Reedy