copyreg.rst

: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_ob=None)

   Declares that *function* should be used as a "reduction" function for objects
   of type *type*.  *function* must return either a string or a tuple
   containing two or five elements. See the :attr:`~pickle.Pickler.dispatch_table`
   for more details on the interface of *function*.

   The *constructor_ob* parameter is a legacy feature and is now ignored, but if
   passed it must be a callable.

   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:
...     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...