On Apr 6, 2016 07:44, "Steven D'Aprano" <st...@pearwood.info> wrote: > > On Wed, Apr 06, 2016 at 11:30:32AM +0200, Petr Viktorin wrote: > > > Python was in a similar situation with the .next method on iterators, > > which changed to __next__ in Python 3. PEP 3114 (which explains this > > change) says: > > > > > Code that nowhere contains an explicit call to a next method can > > > nonetheless be silently affected by the presence of such > > > a method. Therefore, this PEP proposes that iterators should have > > > a __next__ method instead of a next method (with no change in > > > semantics). > > > > How well does that apply to path/__path__? > > I think it's potentially the same. Possibly there are fewer existing > uses of "obj.path" out there which conflict with this use, but there's > at least one in the std lib: sys.path. > > > > That PEP also introduced the next() builtin. This suggests that a > > protocol with __path__/__fspath__ would need a corresponding > > path()/fspath() builtin. > > Not necessarily. Take a look at (say) dir(object()) and you'll see a few > dunders that don't correspond to built-ins: > > __reduce__ and __reduce_ex__ are used by pickle; > __sizeof__ is used by sys.getsizeof; > __subclasshook__ is used by the ABC system; > > Another example is __trunc__ used by math.trunc(). > > So any such fspath function should stand on its own as a useful > feature, not just because there's a dunder method __fspath__.
An even more precise analogy is provided by __index__, whose semantics are to provide safe casting to integer (the name is a historical accident), as opposed to __int__'s tendency to cast things to integer willy-nilly, including things that really shouldn't be silently accepted as integers. Basically __index__ is to __int__ as __(fs)path__ would be to __str__. There's an operator.index but no builtins.index. -n
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