1764a1765,1805
> .. _customizing-isinstance-issubclass
> 
> Customizing instance and subclass checks
> ----------------------------------------
> 
> .. versionadded:: 2.6
> 
> The following methods are used to override the default behavior of the
> :func:`isinstance` and :func:`issubclass` built-in functions for instances
> (normally, classes) of the classes (normally, metaclasses) implementing them.
> 
> In particular, the metaclass :class:`abc.ABCMeta` implements these methods in
> order to allow the addition of Abstract Base Classes (ABCs) as "virtual base
> classes" to any class or type (including built-in types), and including to
> other ABCs.
> 
> 
> .. method:: object.__instancecheck__(self, instance)
> 
>    Return true if ``instance`` should be considered an instance of ``object``.
>    If defined, called to implement ``isinstance(instance, classinfo)`` when
>    ``object`` is, or is part of, ``classinfo``.
>       
> 
> .. method:: object.__subclasscheck__(self, class)
> 
>    Return true if ``class`` should be considered a subclass of ``object``.
>    If defined, called to implement ``issubclass(class, classinfo)`` when
>    ``object`` is, or is part of, ``classinfo``.
> 
> 
> .. seealso::
> 
>    :pep:`3119` - Introducing Abstract Base Classes
>       Includes the specification for overloading :func:`isinstance` and
>       :func:`issubclass` through :meth:`__instancecheck__` and
>       :meth:`__subclasscheck__`, with motivation for this functionality in the
>       context of adding Abstract Base Classes (see the :mod:`abc` module) to
>       the language.
> 
>