On 3/19/2010 11:43 AM, Terry Reedy wrote:
On 3/19/2010 2:11 PM, Antoine Pitrou wrote:
Raymond Hettinger<raymond.hettinger<at> gmail.com> writes:
The reason to prefer an exception is that decimal/float comparisons are more likely to be a programmer error than an intended behavior.
If you really believe that, then equality comparisons should also be disabled by raising NotImplemented or whatever.
Totally agree. While the example most used in this thread is a less than operator, the text of the thread has never (as far as I have read) distinguished between equality, inequality, or relative signed magnitude comparisons. Sort has also been mentioned explicitly as an example. I perceive that the whole thread is about _all_ comparison operators with one float and one decimal operand currently producing an exception (3.x) or a type-based ordering (2.x). The type-based ordering has been demonstrated to produce unstable sorts in the presence of other types also, so is more of a problem than first perceived, and should be changed.
Clearly, someone who writes 'if somefloat == somedecimal:'assumes (now wrongly) that the test might be true. This is just as buggy as an order comparison. Raising an exception would consistently isolate decimals from other numbers and eliminate the equality intransitivity mess and its nasty effect on sets.
Totally agree.
It still strikes me as a bit crazy for Python to say that 0.0 == 0 and 0 == Decimal(0) but that 0.0 != Decimal(0). Who would expect such a thing?
The same person that would expect both 0 == "0" 0.0 == "0.0" to be False... i.e. anyone that hasn't coded in Perl for too many years. Glenn