Python3: hex() on arbitrary classes

[Philipp Hagemeister]

class X(object):
def __int__(self): return 42
def __hex__(self): return '2b' #sic

hex(X())

What would you expect? Python2 returns '2b', but python 3(74624) throws
TypeError: 'X' object cannot be interpreted as an integer. Why doesn't
python convert the object to int before constructing the hex string?

Regards,

Philipp Hagemeister

[Mark Dickinson]

__hex__ is no longer a magic method in Python 3. If you want to be
able to interpret instances of X as integers in the various Python
contexts that expect integers (e.g., hex(), but also things like list
indexing), you should implement the __index__ method:

Python 3.2a0 (py3k:74624, Sep 1 2009, 16:53:00)
[GCC 4.3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> class X:
... def __index__(self): return 3
...
>>> hex(X())
'0x3'
>>> range(10)[X()]
3
>>> 'abc' * X()
'abcabcabc'

--
Mark

[Philipp Hagemeister]

Mark Dickinson wrote:
> (...) If you want to be

> able to interpret instances of X as integers in the various Python
> contexts that expect integers (e.g., hex(), but also things like list
> indexing), you should implement the __index__ method:

Thanks. Somehow forgot this magic method and deleted it by accident.

Philipp

[Mark Dickinson]

On Sep 1, 5:31 pm, Philipp Hagemeister <phi...@phihag.de> wrote:
> Mark Dickinson wrote:
> > (...) If you want to be
> > able to interpret instances of X as integers in the various Python
> > contexts that expect integers (e.g., hex(), but also things like list
> > indexing), you should implement the __index__ method:
>
> Thanks. Somehow forgot this magic method and deleted it by accident.

I wonder whether it would make sense for the Python 2.x hex
function to fall back to __index__ when __hex__ isn't defined.
With the current setup, it's not clear how to write 2.x code
that will also run (post 2to3 translation) properly on 3.x.

--
Mark