[Python-Dev] total ordering.

[Vladimir 'Yu' Stepanov]

Guido van Rossum wrote:
> On 5/6/06, Vladimir Yu. Stepanov <root at renet.ru> wrote:
> [proposing a total ordering between types]
>
> It Ain't Gonna Happen. (From now on, I'll write this as IAGH.)
>
> In Python 3000, we'll actually *remove* ordering between arbitrary
> types as a feature; only types that explicitly care to be ordered with
> respect to one another will be ordered. Equality tests are unaffected,
> x==y will simply return False if x and y are of incomparable types;
> but x<y (etc.) will raise an exception.
>
> --
> --Guido van Rossum (home page: http://www.python.org/~guido/)
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>   
When comparison is made like ("something" < 123), generating of
exception is necessary. At sorting or use of binary trees it is not
so obvious. The behavior function of comparison in this case
depends on needs of the user. At present time use of redefined
function is complicated.

I shall give an example. By a call of a method sort for the list
can give absolutely different exceptions, depending on the order
of sorted values or data (thanks for David Mertz and Josiah
Carlson):
-----------------------------------------------------------------
> >> [chr(255),1j,1,u't'].sort()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: no ordering relation is defined for complex numbers
> >> [chr(255),1j,u't',1].sort()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xff in position 0: 
ordinal not in range(128)
-----------------------------------------------------------------

If for Python-3000 similar it will be shown concerning types
str(), int(), complex() and so on, and the type of exceptions
will strongly vary, it will make problematic redefinition of
behavior of function of sorting.

It would be quite good to create one more class of exceptions
which would unify generation of mistakes at comparison of
non-comparable types or data.