11.09.18 05:04, Elias Tarhini пише:
This has been bouncing around in my head for a while regarding the
requisite keys() method on mappings:
How come the ** unpacking operator, a built-in language feature, relies
on a non-dunder to operate?
To me, I mean to say, requiring that classes implement keys() – a method
whose name is totally undistinguished – in order to conform to the
mapping protocol feels like a design running counter to Python's norm of
using dunders for everything "hidden". I am not sure if it feels dirty
to anybody else, however. Interestingly, the docs already say
<https://docs.python.org/3/reference/datamodel.html#object.__iter__>
that /[f]or mappings, [__iter__()] should iterate over the keys of the
container/, but it of course is not enforced in any way at present.
So, then — how about enforcing it? Should __iter__(), for the reasons
above, replace the current purpose of keys() in mappings?
I'm not properly equipped at the moment to mess around with CPython
(sorry), but I assume at a minimum this would entail either replacing
all instances of PyMapping_Keys() with PyObject_GetIter()or
alternatively changing PyMapping_Keys() to call the latter.
Does it sound like a reasonable change overall?
Dict has keys(), while list doesn't. If use __iter__() instead of
keys(), {**m} or dict(m) will give unexpected result for some
non-mappings, like m = [0, 2, 1]:
>>> {k: m[k] for k in m}
{0: 0, 2: 1, 1: 2}
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