default object comparison considered harmful?

[A.T.Hofkamp]

On 2008-05-16, Kay Schluehr <kay.schluehr at gmx.net> wrote:
> On 16 Mai, 10:03, "A.T.Hofkamp" <h... at se-162.se.wtb.tue.nl> wrote:
>> Hello all,
>>
>> Yesterday we found the cause of a bug that has caused problems for a long time.
>> It appeared to be the following:
>>
>> class A(object):
>>     pass
>>
>> print min(1.0, A())
>>
>> which is accepted by Python even though the A() object is not numerical in
>> nature.
>>
>> The cause of this behavior seems to be the compare operation of the object
>> class.
>>
>> Is there a way to disable this behavior in Python (other than deriving a new
>> 'object-like' class that doesn't do comparisons?)
>>
>> Sincerely,
>> Albert
>
> Are you sure you don't want to use a statically typed language that
> captures all type errors just by inspecting your source code?

yes.

The problem here is that it isn't caught at all, neither at 'compile' time nor
at run-time. That means that the Python language considers this proper code.

Whether you make that decision by inspecting source code or at run-time is
irrelevant here.


Unfortunaly, we have to maintain Python 2.3 compability.
As a solution, I have created a new BaseObject class as follows:

class BaseObject(object):
    """
    Generic base class without default compare and hashing functions.
    """
    def __cmp__(self, other):
        """ Disable default compare method """
        raise NotImplementedError

    def __hash__(self):
        """ Disable default hashing method """
        raise NotImplementedError("Implement me in class '%s'"
                                                    % self.__class__.__name__)


Sincerely,
Albert