Re: [BangPypers] Python comparisons

[Gora Mohanty]

On 5 December 2015 at 12:56, Noufal Ibrahim KV  wrote:
>
>
> So I came across this today..
>
> >>> class Number(object):
> ...def __init__(self, n):
> ...   self.n = n
> ...
> >>> m = Number(10)
> >>> n = Number(5)
> >>>
> >>> m < n
> True
>
> This is documented like so
>
> > If no __cmp__(), __eq__() or __ne__() operation is defined, class
> > instances are compared by object identity (“address”).
>
> over here https://docs.python.org/2/reference/datamodel.html#object.__cmp__

Maybe because that was the historical way that C did it? I agree that
the Python 3 exception makes more sense.

Regards,
Gora
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Re: [BangPypers] Python comparisons

[Noufal Ibrahim KV]

On Sat, Dec 05 2015, Gora Mohanty wrote:


[...]

> Maybe because that was the historical way that C did it? I agree that
> the Python 3 exception makes more sense.

[...]

We can only guess but you'll have to explicitly code this in and I can't
think of any situation where it would make sense.


-- 
Cordially,
Noufal
http://nibrahim.net.in
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Re: [BangPypers] Python comparisons

[Noufal Ibrahim KV]

On Sat, Dec 05 2015, Anand Chitipothu wrote:


[...]

> Thats why you should use Python 3. Here is what you get with Python 3.

[...]

Yet another reason to move. I'm still curious why they did it the other
way in 2.x though.


-- 
Cordially,
Noufal
http://nibrahim.net.in
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Re: [BangPypers] Python comparisons

[Anand Chitipothu]

On Sat, Dec 5, 2015 at 12:56 PM, Noufal Ibrahim KV 
wrote:

>
> So I came across this today..
>
> >>> class Number(object):
> ...def __init__(self, n):
> ...   self.n = n
> ...
> >>> m = Number(10)
> >>> n = Number(5)
> >>>
> >>> m < n
> True
>
> This is documented like so
>
> > If no __cmp__(), __eq__() or __ne__() operation is defined, class
> > instances are compared by object identity (“address”).
>
> over here
> https://docs.python.org/2/reference/datamodel.html#object.__cmp__
>
> It seems a rather arbitrary thing to do. Why is it implemented at all?
> I'd expect it to just break with a TypeError similar to what would
> happen if I do
>
> >>> m + n
> Traceback (most recent call last):
>   File "", line 1, in 
> TypeError: unsupported operand type(s) for +: 'Number' and 'Number'
> >>>
>

Thats why you should use Python 3. Here is what you get with Python 3.

>>> class Foo: pass
...
>>> a = Foo()
>>> b = Foo()
>>>
>>> a < b
Traceback (most recent call last):
  File "", line 1, in 
TypeError: unorderable types: Foo() < Foo()

That would give True in Python 2.

Anand
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[BangPypers] Python comparisons

[Noufal Ibrahim KV]

So I came across this today..

>>> class Number(object):
...def __init__(self, n):
...   self.n = n
... 
>>> m = Number(10)
>>> n = Number(5)
>>> 
>>> m < n
True

This is documented like so

> If no __cmp__(), __eq__() or __ne__() operation is defined, class
> instances are compared by object identity (“address”).

over here https://docs.python.org/2/reference/datamodel.html#object.__cmp__

It seems a rather arbitrary thing to do. Why is it implemented at all?
I'd expect it to just break with a TypeError similar to what would
happen if I do

>>> m + n
Traceback (most recent call last):
  File "", line 1, in 
TypeError: unsupported operand type(s) for +: 'Number' and 'Number'
>>> 


-- 
Cordially,
Noufal
http://nibrahim.net.in
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