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

[Rustom Mody]

On Monday, February 2, 2015 at 9:34:53 AM UTC+5:30, Rustom Mody wrote:
> 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()

Well I continue to be fooled

>>> d1 = {k:getattr([],k) for k in [].__dir__()}

>>> d2 = {k:getattr([],k) for k in dir([])}
>>> d1 == d2
False

>>> len(d1)
45
>>> len(d2)
45

>>> d1.keys()
dict_keys(['__rmul__', '__str__', '__gt__', '__mul__', '__class__', '__ne__', '__format__', '__sizeof__', '__contains__', '__imul__', '__add__', 'sort', 'count', 'extend', 'remove', '__init__', 'insert', '__setitem__', 'index', '__subclasshook__', 'copy', '__getitem__', '__iadd__', '__hash__', '__delitem__', '__reduce_ex__', '__iter__', '__repr__', '__le__', '__setattr__', 'reverse', '__new__', '__eq__', '__len__', '__doc__', '__lt__', 'clear', '__ge__', 'append', '__dir__', '__reversed__', '__getattribute__', 'pop', '__delattr__', '__reduce__'])
>>> d1.keys() == d2.keys()
True