[python] (fork) object proxying

fn.py

## Based on http://code.activestate.com/recipes/519639/ (r1)
##      and http://code.activestate.com/recipes/496741-object-proxying/ (r1)

import copy

def proxy(cls, target):
    """
    A, the class of the object to be proxied, intentionally takes an argument.
    This foils any proxy techniques that instantiate the class of the proxee.

    Yet there is no relation between its constructor's arity and any objects
    that desire to proxy it.
    >>> class A(object):
    ...     def __init__(self, bar, _):
    ...         print 'A init'
    ...         self.bar = bar
    ...         super(A, self).__init__()
    ...     def foobar(self):
    ...         print 'A foobar', self.bar
    ... 

    B, the class of the proxy object, may have a constructor that takes
    arguments, but this proxy technique pays no regard to it.
    >>> class B(object):
    ...     def __init__(self, a, b):
    ...         print 'B init, not'
    ...     def foobar(self):
    ...         print 'B foobar'
    ...         super(B, self).foobar()
    ... 
    >>> class C(object):
    ...     pass
    ... 
    >>> a = A(1, "hello")
    A init
    >>> a.foobar()
    A foobar 1
    >>> a.baz = 5
    >>> b = proxy(B, a)
    >>> c = proxy(C, b)

    Changes to the object being proxied are *not* available to the proxy:
    >>> a.bar = 3
    >>> a.foobar()
    A foobar 3
    >>> b.foobar()
    B foobar
    A foobar 1

    Attributes on the proxy shadow the object being proxied:
    >>> a.foobar()
    A foobar 3
    >>> b.bar = 2
    >>> a.foobar()
    A foobar 3
    >>> b.foobar()
    B foobar
    A foobar 2

    Attributes added to the object being proxied before instantiating the
    proxy are available:
    >>> b.baz
    5
    >>> c.baz
    5

    Not so for attributes added after instantiating:
    >>> a.bax = 4
    >>> b.bax
    Traceback (most recent call last):
      ...
    AttributeError: 'B(A)' object has no attribute 'bax'
    """

    ins = copy.copy(target)
    target_cls = type(ins)
    ins.__class__ = type("%s(%s)" % (cls.__name__, target_cls.__name__), (cls, target_cls), {})
    return ins

kls.py

## Based on http://code.activestate.com/recipes/519639/ (r1)
##      and http://code.activestate.com/recipes/496741-object-proxying/ (r1)

from types import MethodType

class Proxy(object):
    """
    A, the class of the object to be proxied, intentionally takes an argument.
    This foils any proxy techniques that instantiate the class of the proxee.

    Yet there is no relation between its constructor's arity and any objects
    that desire to proxy it.
    >>> class A(object):
    ...     def __init__(self, bar, _):
    ...         print 'A init'
    ...         self.bar = bar
    ...         super(A, self).__init__()
    ...     def foobar(self):
    ...         print 'A foobar', self.bar
    ... 

    B, the class of the proxy object, if it is to have a constructor, must take
    an argument, due to its parentage (the Proxy class).
    >>> class B(Proxy):
    ...     def __init__(self, target):
    ...         print 'B init'
    ...         super(B, self).__init__(target)
    ...     def foobar(self):
    ...         print 'B foobar'
    ...         super(B, self).foobar()
    ... 
    >>> class C(Proxy):
    ...     def __init__(self, target):
    ...         print 'C init'
    ...         super(C, self).__init__(target)
    ... 
    >>> a = A(1, "hello")
    A init
    >>> a.foobar()
    A foobar 1
    >>> a.baz = 5
    >>> b = B(a)
    B init
    >>> c = C(b)
    C init
    B init

    Changes to the object being proxied are available to the proxy:
    >>> a.bar = 3
    >>> a.foobar()
    A foobar 3
    >>> b.foobar()
    B foobar
    A foobar 3

    Attributes on the proxy shadow the object being proxied:
    >>> a.foobar()
    A foobar 3
    >>> b.bar = 2
    >>> a.foobar()
    A foobar 3
    >>> b.foobar()
    B foobar
    A foobar 2

    Attributes added to the object being proxied before instantiating the
    proxy are available:
    >>> b.baz
    5
    >>> c.baz
    5

    This holds for attributes added after instantiating:
    >>> a.bax = 4
    >>> b.bax
    4
    """

    # for orthogonal __init__'s()
    def __init__(self, target):
        pass

    def __new__(cls, target, *args, **kwargs):
        target_cls = type(target)
        newcls = type("%s(%s)" % (cls.__name__, target_cls.__name__),
            (cls, target_cls),
            dict(__getattr__=lambda self, name: getattr(target, name)))
        ins = super(Proxy, newcls).__new__(newcls)
        return ins