[issue20751] Misleading examples indDescriptor protocol documentation

[Jan Kaliszewski]

New submission from Jan Kaliszewski:

1. One misleading detail in the descriptor protocol documentation for super bindings is that the following fragment of the http://docs.python.org/reference/datamodel.html#invoking-descriptors page:

"""
Super Binding
    If a is an instance of super, then the binding super(B, obj).m() searches obj.__class__.__mro__ for the base class A immediately preceding B and then invokes the descriptor with the call: A.__dict__['m'].__get__(obj, obj.__class__).
"""

...introduces the method *call* (".m()") which AFAIK has nothing to do with the actual matter of the description (attribute resolution).

Also, the "If *a* is an instance of super" fragment is strange, as *a* is not used in the following sentences at all.

I believe the description should be:

"""
Super Binding
    If binding to a super instance, super(B, obj).x searches obj.__class__.__mro__ for the base class A immediately preceding B and then invokes the descriptor with the call: A.__dict__['x'].__get__(obj, obj.__class__).
"""

(using 'x' as the attribute name, as for the other kinds of binding).

***

2. Also, in some earlier fragment of the same page:

"""
Direct Call
    The simplest and least common call is when user code directly invokes a descriptor method: x.__get__(a).
"""

The call x.__get__(a) without the second argument seems to be wrong if  __get__ is implemented according to the specification "object.__get__(self, instance, owner)" from the same documentation page.

----------
assignee: docs at python
components: Documentation
messages: 212035
nosy: docs at python, zuo
priority: normal
severity: normal
status: open
title: Misleading examples indDescriptor protocol documentation
versions: Python 2.7, Python 3.1, Python 3.2, Python 3.3, Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue20751>
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