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python-3.7.4-docs-html/_sources/library/copyreg.rst.txt

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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::
+   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=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.
+
+   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.  :exc:`TypeError` will be raised if
+   *object* is a class or *constructor* is not callable.
+
+   See the :mod:`pickle` module for more details on the interface
+   expected of *function* and *constructor*.  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(object):
+   ...     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...