Arbitrary dunder attributes (was Re: odd difference calling function from class or instance variable)

[Ned Batchelder]

On 8/13/14 5:51 AM, Chris Angelico wrote:
> On Wed, Aug 13, 2014 at 7:06 PM, GregS <not at my.real.address.com> wrote:
>> When I assign the reference as a class variable, the reference has __self__
>> set, too, so I get an extra argument passed to the function.  If I assign
>> the reference as an instance variable, then __self__ is unset so no extra
>> argument.
>
> Spin-off from Greg's thread.
>
> The bound method object stores a reference to the original object (the
> thing that becomes the first argument to the target function) in
> __self__ (and the function in __func__). ISTM this ought to be _self
> (and _func), as it's intended to be private; is it really something
> that has language-level significance on par with __lt__ and so on?
>
> ChrisA
>

As I see it, dunder names are those whose meaning is defined by the 
Python language (and/or implementation?), and whose use is typically 
behind-the-scenes.  So "len" is defined by the language, but is meant to 
be front-and-center, so it has a nice name.  __init__, __lt__, and 
__self__, have meanings and uses defined by Python itself, and so are 
reasonable as dunder names.

This is a crude namespacing: Python can use any name it likes so long as 
its a dunder name, and I can use any name I like, so long as it isn't.

Yes, the definition is fuzzy.... :)

-- 
Ned Batchelder, http://nedbatchelder.com