New submission from Aaron Hall:
Based on the data-model documentation
(https://docs.python.org/2/reference/datamodel.html#invoking-descriptors) and
the dotted lookup behavior, the follow definitions are correct:
"If the descriptor defines __set__() and/or __delete__(), it is a data
descriptor; if it defines neither, it is a non-data descriptor."
def has_data_descriptor_attrs(obj):
return set(['__set__', '__delete__']) & set(dir(obj))
def is_data_descriptor(obj):
return bool(has_data_descriptor_attrs(obj))
However, the inspect module has the following, which is also reflected in the
descriptor how-to
(https://docs.python.org/2/howto/descriptor.html#descriptor-protocol):
"If an object defines both __get__() and __set__(), it is considered a data
descriptor."
def isdatadescriptor(object):
"""Return true if the object is a data descriptor.
Data descriptors have both a __get__ and a __set__ attribute..."""
if isclass(object) or ismethod(object) or isfunction(object):
# mutual exclusion
return False
tp = type(object)
return hasattr(tp, "__set__") and hasattr(tp, "__get__")
I'm willing to sign a contributor release and fix myself.
----------
messages: 258168
nosy: Aaron Hall
priority: normal
severity: normal
status: open
title: Contradiction in definition of "data descriptor" between (dotted lookup
behavior/datamodel documentation) and (inspect lib/descriptor how-to)
type: behavior
versions: Python 2.7, Python 3.2, Python 3.3, Python 3.4, Python 3.5, Python 3.6
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Python tracker <[email protected]>
<http://bugs.python.org/issue26103>
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