On 10/13/2013 04:44 AM, Nick Coghlan wrote:
On 13 Oct 2013 08:27, "Ethan Furman" <[email protected]> wrote:
It was pointed in Issue16938[1] that __objclass__ is not documented anywhere.
Is the following an appropriate description? (in Doc/reference/datamodel.rst in
user-defined functions)
+-------------------------+-------------------------------+-----------+
| :attr:`__objclass__` | The class this object belongs | |
| | to; useful when the object is | |
| | a descriptor, or a virtual or | |
| | dynamic class attribute, and | |
| | it's __class__ attribute does | |
| | not match the class it is | |
| | associated with, or it is not | |
| | in that class' ``__dict__``. | |
+-------------------------+-------------------------------+-----------+
I think this is inaccurate. The meaning of __objclass__ as described
in PEP 252 is to denote unbound callable descriptors that only work
with a specific type. That's why it's mostly gone in Python 3.
PEP 252 has this comment:
[Editor's note: the ideas described in this PEP have been incorporated
into Python. The PEP no longer accurately describes the implementation.]
It should be documented, but the documentation should say something like:
__objclass__: Indicates this callable requires an instance of the
given type (or a subclass) as its first positional argument. For
example, CPython sets this for unbound methods that are implemented in
C rather than Python.
The offending block of code in the inspect module
(http://hg.python.org/cpython/file/default/Lib/inspect.py#l366) that
prompted http://bugs.python.org/issue16938 just looks flat out broken
to me. There's *zero* reason to expect that __class__ on the result of
retrieving an attribute from an object will appear in the MRO for that
object. I just missed that detail when reviewing
http://bugs.python.org/issue19030 :)
Actually, it's the other way around -- the code currently in inspect.py at that point was prompted by this issue (and
tracked in Issue 19030). Interestingly enough, with the current changes in 16938 I can remove the __objclass__
attribute I had added to Enum to get around this.
--
~Ethan~
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