dunder-docs (was Python is DOOMED! Again!)

[Rustom Mody]

On Monday, February 2, 2015 at 9:22:51 AM UTC+5:30, Rustom Mody wrote:
> On Sunday, February 1, 2015 at 9:51:11 PM UTC+5:30, Steven D'Aprano wrote:
> > Rustom Mody wrote:
> > 
> > > The other day I was taking a class in which I was showing
> > > - introspection for discovering -- help, type, dir etc at the repl
> > > - mapping of surface syntax to internals eg. a + b ←→ a.__add__(b)
> > > 
> > > And a student asked me the diff between
> > > dir([])
> > > and
> > > [].__dir__()
> > > 
> > > I didnt know what to say...
> > 
> > Surely the right answer would have been "I don't know, let's check the
> > interactive interpreter first, and the docs second."
> > 
> > Checking the REPL first would have revealed that [].__dir__ raises
> > AttributeError. In other words, lists don't have a __dir__ method.
> 
> ??
> 
> $ python3
> Python 3.4.2 (default, Oct  8 2014, 13:08:17) 
> [GCC 4.9.1] on linux
> Type "help", "copyright", "credits" or "license" for more information.
> >>> [].__dir__
> <built-in method __dir__ of list object at 0x7f5dd2209f48>
> >>> dir([])
> ['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']
> >>> [].__dir__()
> ['__rmul__', '__str__', '__gt__', 'remove', '__class__', '__getitem__', '__format__', '__ne__', '__sizeof__', '__contains__', '__reduce__', '__add__', 'sort', 'count', 'extend', '__mul__', '__imul__', '__reduce_ex__', '__setitem__', '__doc__', '__ge__', 'copy', '__init__', '__iadd__', '__hash__', '__delitem__', 'insert', '__iter__', '__repr__', '__le__', '__setattr__', 'reverse', '__new__', '__eq__', '__len__', 'index', '__lt__', 'clear', '__subclasshook__', 'append', '__dir__', '__reversed__', '__getattribute__', 'pop', '__delattr__']
> >>> 
> 
> What you are describing seems to be true for python2 though

And since they *looked* different I believed they were different.

Evidently not…

>>> s1= set([].__dir__())
>>> s2=set(dir([]))
>>> s1
{'__rmul__', '__str__', '__class__', '__ne__', '__repr__', '__format__', '__sizeof__', '__contains__', '__add__', 'sort', 'count', 'extend', 'remove', '__mul__', '__reduce__', '__imul__', '__reduce_ex__', '__setitem__', 'insert', '__doc__', '__ge__', 'index', 'copy', '__subclasshook__', '__getitem__', '__init__', '__iadd__', '__hash__', '__delitem__', '__iter__', '__le__', '__setattr__', 'reverse', '__new__', '__eq__', '__len__', '__lt__', 'clear', '__gt__', 'append', '__dir__', '__reversed__', '__getattribute__', 'pop', '__delattr__'}
>>> s2
{'__rmul__', '__str__', '__class__', '__ne__', '__repr__', '__format__', '__sizeof__', '__contains__', '__add__', 'sort', 'count', 'extend', '__mul__', 'remove', '__imul__', '__reduce__', '__reduce_ex__', '__setitem__', 'insert', '__doc__', '__ge__', '__subclasshook__', 'copy', 'index', '__getitem__', '__iadd__', '__init__', '__hash__', '__delitem__', '__iter__', '__le__', '__setattr__', 'reverse', '__new__', '__eq__', '__len__', '__lt__', 'clear', '__gt__', 'append', '__dir__', '__reversed__', '__getattribute__', 'pop', '__delattr__'}
>>> len(s1)
45
>>> len(s2)
45
>>> s1 - s2
set()
>>> s2 - s1
set()