# `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_ob=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. See the `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 `dispatch_table` attribute of a pickler object or subclass of `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)
    pickling a C instance...
    >>> p = pickle.dumps(c)
    pickling a C instance...