:mod:`copyreg` --- Register :mod:`pickle` support functions

.. module:: copyreg
 :synopsis: Register pickle support functions.

Source code: :source:`Lib/copyreg.py`

.. index::
 module: pickle
 module: copy

The :mod:`copyreg` module offers a way to define functions used while pickling specific objects. The :mod:`pickle` and :mod:`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.

.. function:: constructor(object)

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

.. function:: 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. :exc:`TypeError` will be raised if
 *object* is a class or *constructor* is not callable.

 See the :mod:`pickle` module for more details on the interface
 expected of *function* and *constructor*. Note that the
 :attr:`~pickle.Pickler.dispatch_table` attribute of a pickler
 object or subclass of :class:`pickle.Pickler` can also be used for
 declaring reduction functions.

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) # doctest: +SKIP
pickling a C instance...
>>> p = pickle.dumps(c) # doctest: +SKIP
pickling a C instance...

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