11.3. "copy_reg" — Register "pickle" support functions
******************************************************

Note:

  The "copy_reg" module has been renamed to "copyreg" in Python 3. The
  *2to3* tool will automatically adapt imports when converting your
  sources to Python 3.

The "copy_reg" module offers a way to define functions used while
pickling specific objects.  The "pickle", "cPickle", and "copy"
modules use those functions when pickling/copying those objects.  The
module provides configuration information about object constructors
which are not classes. Such constructors may be factory functions or
class instances.

copy_reg.constructor(object)

   Declares *object* to be a valid constructor.  If *object* is not
   callable (and hence not valid as a constructor), raises
   "TypeError".

copy_reg.pickle(type, function[, constructor])

   Declares that *function* should be used as a “reduction” function
   for objects of type *type*; *type* must not be a “classic” class
   object.  (Classic classes are handled differently; see the
   documentation for the "pickle" module for details.)  *function*
   should return either a string or a tuple containing two or three
   elements.

   The optional *constructor* parameter, if provided, is a callable
   object which can be used to reconstruct the object when called with
   the tuple of arguments returned by *function* at pickling time.
   "TypeError" will be raised if *object* is a class or *constructor*
   is not callable.

   See the "pickle" module for more details on the interface expected
   of *function* and *constructor*.


11.3.1. Example
===============

The example below would like to show how to register a pickle function
and how it will be used:

>>> import copy_reg, copy, pickle
>>> class C(object):
...     def __init__(self, a):
...         self.a = a
...
>>> def pickle_c(c):
...     print("pickling a C instance...")
...     return C, (c.a,)
...
>>> copy_reg.pickle(C, pickle_c)
>>> c = C(1)
>>> d = copy.copy(c)
pickling a C instance...
>>> p = pickle.dumps(c)
pickling a C instance...
