[docs] Wrong function calls and referring to not removed concepts in descriptor HowTo (documentation) (issue 25435)

[vadmium+py at gmail.com]

http://bugs.python.org/review/25435/diff/15789/Doc/howto/descriptor.rst
File Doc/howto/descriptor.rst (right):

http://bugs.python.org/review/25435/diff/15789/Doc/howto/descriptor.rst#newcode283
Doc/howto/descriptor.rst:283: self.f = f
I reckon leave this bit out. It is meant to represent the actual
function class, not a wrapper.

http://bugs.python.org/review/25435/diff/15789/Doc/howto/descriptor.rst#newcode287
Doc/howto/descriptor.rst:287: if obj is Null:
None not Null

http://bugs.python.org/review/25435/diff/15789/Doc/howto/descriptor.rst#newcode289
Doc/howto/descriptor.rst:289: return self.f
return self

http://bugs.python.org/review/25435/diff/15789/Doc/howto/descriptor.rst#newcode292
Doc/howto/descriptor.rst:292: return types.MethodType(self.f, obj)
MethodType(self, obj)

http://bugs.python.org/review/25435/diff/15789/Doc/howto/descriptor.rst#newcode303
Doc/howto/descriptor.rst:303: >>> D.f             # Get from a class
becomes a function as well
Get from a class returns the same function

http://bugs.python.org/review/25435/diff/15789/Doc/howto/descriptor.rst#newcode308
Doc/howto/descriptor.rst:308: The output suggests that bound and unbound
methods are two different types.
This whole paragraph could be removed IMO. In Python 3, “self” is not
allowed to be None, and unbound methods are the original function
object.

http://bugs.python.org/review/25435/diff/15789/Doc/howto/descriptor.rst#newcode315
Doc/howto/descriptor.rst:315: field. If set (meaning bound), the
original function (stored in the
The only Python 3 relevant bit is the second sentence I think. The rest
could be dropped.

http://bugs.python.org/review/25435/diff/15789/Doc/howto/descriptor.rst#newcode318
Doc/howto/descriptor.rst:318: function. The actual C implementation of
:func:`instancemethod_call()` is only
instancemethod_call seems to be a method of PyInstanceMethod_Type, which
is part of the C API, but doesn’t seem to be used at all. Don’t think it
is worth mentioning.

http://bugs.python.org/review/25435/