Comparison of functions

[Adriano Varoli Piazza]

Steven D'Aprano ha scritto:
> On Sat, 30 Jul 2005 08:13:26 -0400, Peter Hansen wrote:
> 
> 
>>Beginners should not be comparing lambdas.
>>
>>Neither should you. ;-)
> 
> 
> Actually, yes I should, because I'm trying to make sense of the mess that
> is Python's handling of comparisons. At least two difference senses of
> comparisons is jammed into one, leading to such such warts as these:
> 
> 
>>>>L = []
>>>>L.sort()  # we can sort lists
>>>>L.append(1+1j)
>>>>L.sort()  # even if they include a complex number
>>>>L.append(1)
>>>>L.sort()  # but not any more
> 
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> TypeError: cannot compare complex numbers using <, <=, >, >=
> 
> Um, I didn't ask to compare complex numbers using comparison operators. I
> asked to sort a list. And please don't tell me that that sorting is
> implemented with comparison operators. That just means that the
> implementation is confusing numeric ordering with sort order.
> 
> Then there is this:
> 
> 
>>>>1 > 0
> 
> True
> 
>>>>1+0j == 1
> 
> True
> 
>>>>1+0j == 1 > 0
> 
> True
> 
>>>>1+0j > 0
> 
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> TypeError: cannot compare complex numbers using <, <=, >, >=
> 
> I applaud that Python has got rich comparisons for those who need them.
> But by confusing the question "which comes first in a sorted list?" with
> "which is larger?", you get all sorts of warts like being unable to sort
> lists with some objects, while being able to make meaningless
> comparisons like ''.join >= [].append.
> 
> I'm not sure what the solution to this ugly state of affairs is. I'm not
> even sure if there is a solution. But I'm willing to make a good effort to
> *look*, and even though you were joking, I don't appreciate being told
> not to.

As far as I recall from Math Analysis, which I studied two months ago, 
you can't sort complex numbers. It makes no sense. The reason being 
(reading from my book), it's not possible to define an order that 
preserves the properties of arithmetical operations on complex numbers. 
So you can't order them, and you can't compare them.


-- 
Adriano Varoli Piazza
The Inside Out: http://moranar.com.ar
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