__abs(self)__?

[Sean 'Shaleh' Perry]

On 01-Mar-2002 Mike Carifio wrote:
> I'm reading about special method names. __abs__(self), which maps to the
> abs() method seems unneccessary(?).
> So:
> 
> class ExampleNumber:
>     def __init__(self, initializer):
>         self.value = initializer
>     def __abs__(self):
>         return abs(self.value)
> 
>>>> x = ExampleNumber(-1)
>>>> x.abs()
> 1
> 
> seems no different from:
> 
> class ExampleNumber:
>     def __init__(self, initializer):
>         self.value = initializer
>     def abs(self):   # name isn't special?
>         return abs(self.value)
> 
> abs is a builtin function, so why do I need a special name for a function?
> I'm missing something...
> 

the __foo__ method names are special because you do not call them directly
(usually) rather they are triggered when a request is made.

__abs__() causes the object to return a value that represents the absolute
value of the object's data, whatever that means.

abs(obj) translates into obj.__abs__().  This is just like 'print obj' calling
obj.__str__() or 'obj[i]' calling obj.__getitem__(i).