1:mod:`copy_reg` --- Register :mod:`pickle` support functions
2============================================================
3
4.. module:: copy_reg
5   :synopsis: Register pickle support functions.
6
7.. note::
8   The :mod:`copy_reg` module has been renamed to :mod:`copyreg` in Python 3.
9   The :term:`2to3` tool will automatically adapt imports when converting your
10   sources to Python 3.
11
12.. index::
13   module: pickle
14   module: cPickle
15   module: copy
16
17The :mod:`copy_reg` module offers a way to define functions used while pickling
18specific objects.  The :mod:`pickle`, :mod:`cPickle`, and :mod:`copy` modules
19use those functions when pickling/copying those objects.  The module provides
20configuration information about object constructors which are not classes.
21Such constructors may be factory functions or class instances.
22
23
24.. function:: constructor(object)
25
26   Declares *object* to be a valid constructor.  If *object* is not callable (and
27   hence not valid as a constructor), raises :exc:`TypeError`.
28
29
30.. function:: pickle(type, function[, constructor])
31
32   Declares that *function* should be used as a "reduction" function for objects of
33   type *type*; *type* must not be a "classic" class object.  (Classic classes are
34   handled differently; see the documentation for the :mod:`pickle` module for
35   details.)  *function* should return either a string or a tuple containing two or
36   three elements.
37
38   The optional *constructor* parameter, if provided, is a callable object which
39   can be used to reconstruct the object when called with the tuple of arguments
40   returned by *function* at pickling time.  :exc:`TypeError` will be raised if
41   *object* is a class or *constructor* is not callable.
42
43   See the :mod:`pickle` module for more details on the interface expected of
44   *function* and *constructor*.
45
46Example
47-------
48
49The example below would like to show how to register a pickle function and how
50it will be used:
51
52   >>> import copy_reg, copy, pickle
53   >>> class C(object):
54   ...     def __init__(self, a):
55   ...         self.a = a
56   ...
57   >>> def pickle_c(c):
58   ...     print("pickling a C instance...")
59   ...     return C, (c.a,)
60   ...
61   >>> copy_reg.pickle(C, pickle_c)
62   >>> c = C(1)
63   >>> d = copy.copy(c)
64   pickling a C instance...
65   >>> p = pickle.dumps(c)
66   pickling a C instance...
67