11.3. copy_reg — Register pickle support functions


The copy_reg module has been renamed to copyreg in Python 3. The 2to3 tool will automatically adapt imports when converting your sources to Python 3.

The copy_reg module offers a way to define functions used while pickling specific objects. The pickle, cPickle, 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.


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

copy_reg.pickle(type, function[, constructor])

Declares that function should be used as a “reduction” function for objects of type type; type must not be a “classic” class object. (Classic classes are handled differently; see the documentation for the pickle module for details.) 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. TypeError will be raised if object is a class or constructor is not callable.

See the pickle module for more details on the interface expected of function and constructor.

11.3.1. Example

The example below would like to show how to register a pickle function and how it will be used:

>>> import copy_reg, 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,)
>>> copy_reg.pickle(C, pickle_c)
>>> c = C(1)
>>> d = copy.copy(c)
pickling a C instance...
>>> p = pickle.dumps(c)
pickling a C instance...

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