copyreg — Register pickle support functions (original) (raw)

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 must return either a string or a tuple containing between two and six elements. See the dispatch_tablefor 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...