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:mod:`copyreg` --- Register :mod:`pickle` support functions
===========================================================
.. module:: copyreg
:synopsis: Register pickle support functions.
**Source code:** :source:`Lib/copyreg.py`
.. index::
pair: module; pickle
pair: 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 between two and six 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...
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