12.2. "copyreg" — Register "pickle" support functions
*****************************************************

**Source code:** Lib/copyreg.py

======================================================================

The "copyreg" module offers a way to define functions used while
pickling specific objects.  The "pickle" 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.

copyreg.constructor(object)

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

copyreg.pickle(type, function, constructor=None)

   Declares that *function* should be used as a “reduction” function
   for objects of type *type*.  *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*.  Note that the "dispatch_table"
   attribute of a pickler object or subclass of "pickle.Pickler" can
   also be used for declaring reduction functions.


12.2.1. Example
===============

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

>>> import copyreg, 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,)
...
>>> copyreg.pickle(C, pickle_c)
>>> c = C(1)
>>> d = copy.copy(c)
pickling a C instance...
>>> p = pickle.dumps(c)
pickling a C instance...
