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



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[Mark Dickinson]

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?

__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..... def __index__(self): return 3
....

hex(X()) '0x3'
range(10)[X()] 3
'abc' * X()

'abcabcabc'

 

[Philipp Hagemeister]

(...) 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

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.... def __index__(self): return 3
...

hex(X()) '0x3'
range(10)[X()] 3
'abc' * X()

'abcabcabc'

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[Mark Dickinson]

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.