def freeze(obj):
    try:
        hash(obj)
        return obj
    except TypeError:
        freezer = getattr(obj, '__freeze__', None)
        if freezer:
            return freezer()
        raise TypeError('object is not freezable')``

class xset(set):
    def __freeze__(self):
        return frozenset(self)

class xlist(list):
    def __freeze__(self):
        return tuple(self)

class imdict(dict):
    def __hash__(self):
        return id(self)

    def _immutable(self, *args, **kws):
        raise TypeError('object is immutable')

    __setitem__ = _immutable
    __delitem__ = _immutable
    clear       = _immutable
    update      = _immutable
    setdefault  = _immutable
    pop         = _immutable
    popitem     = _immutable

class xdict(dict):
    def __freeze__(self):
        return imdict(self)

>>> s = set([1, 2, 3])
>>> {s: 4}
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: set objects are unhashable
>>> t = freeze(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/tmp/python-lWCjBK.py", line 9, in freeze
TypeError: object is not freezable
>>> t = xset(s)
>>> u = freeze(t)
>>> {u: 4}
{frozenset([1, 2, 3]): 4}
>>> x = 'hello'
>>> freeze(x) is x
True
>>> d = xdict(a=7, b=8, c=9)
>>> hash(d)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: dict objects are unhashable
>>> hash(freeze(d))
-1210776116
>>> {d: 4}
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: dict objects are unhashable
>>> {freeze(d): 4}
{{'a': 7, 'c': 9, 'b': 8}: 4}