a proxy wrapper for objects that lazily creates object copies on simple attribution of the object to other variables.

autocopyproxy.py

# copyright Joao S. O. Bueno (2015)
# License: # SVP write me if you intend to reuse stuff here for anything but mayhem
# There is an LGPL with lazyobjects based on this idea for proxy at
# bitbucket.org/jsbueno/metapython [lazy_decorator.py]


# NB: although there is support for inspecting Frames - this works only
# for global variables
# working for Python2 - for python3 onlye the metaclass usage should need to be changed


import gc, types
from copy import copy

from functools import wraps

data_model_methods = """
    __repr__ __str__ __cmp__
    __hash__  __nonzero__
    __delattr__
    __call__
    __len__ __getitem__ __setitem__ __delitem__ __reversed__ __contains__
    __add__ __sub__ __mul__ __floordiv__ __mod__ __divmod__ __pow__  __div__ __truediv__
    __lshift__  __rshift__ __and__ __xor__ __or__
    __radd__ __rsub__ __rmul__ __rfloordiv__ __rmod__ __rdivmod__
    __rpow__ __rdiv__ __rtruediv__
    __rlshift__  __rrshift__ __rand__ __rxor__ __ror__
    __iadd__ __isub__ __imul__ __ifloordiv__ __imod__  __ipow__ __idiv__ __itruediv__
    __ilshift__  __irshift__ __iand__ __ixor__ __ior__
    __neg__ __pos__ __abs__ __invert__
    __complex__ __int__ __long__ __float__
    __oct__ __hex__
    __index__ __coerce__
""".split()


def auto_copy_decorator(method):
    wraps(method)
    instances = {}
    def wrapper(self, *args, **kw):
        self = self._do_the_thing()
        return getattr(self._proxied.__class__, method)(self._proxied, *args, **kw)
    return wrapper

class MetaAutoCopyProxy(type):
    def __new__(metacls, name, bases, dct):
        for key in data_model_methods:
            dct[key] = auto_copy_decorator(key)
        return type.__new__(metacls, name, bases, dct)

class AutoCopyProxy(object):
    __metaclass__ = MetaAutoCopyProxy
    def __init__(self, proxied):
        self._proxied = proxied
        self._instances = {}
        
    def _do_the_thing(self):
        first_copy = True
        new_self = self
        for ref in gc.get_referrers(self):
            if isinstance(ref, types.FrameType):
                ref = ref.f_locals
            elif isinstance(ref, dict):
                pass
            else:
                continue
            for key, value in ref.items():
                if value is self:
                    if first_copy:
                        first_copy = False
                        continue
                    new_self = AutoCopyProxy(copy(self._proxied))
                    # Changeling thing:
                    ref[key] = new_self
        return new_self
            
        
    def __getattribute__(self, attr):
        if attr not in ("__init__", "_instances", "_proxied", "_do_the_thing"):
            self = self._do_the_thing()
            return getattr(self._proxied, attr)
        return object.__getattribute__(self, attr)

gistfile1.py

"""
>>> from autocopyproxy import AutoCopyProxy as A
>>> x = A([])
>>> y = x
>>> y is x
True
>>> y.append(5)
>>> x
[]
>>> y
[5]
>>> y is x
False
"""