summaryrefslogtreecommitdiff
path: root/Doc/library/copy.rst
diff options
context:
space:
mode:
Diffstat (limited to 'Doc/library/copy.rst')
-rw-r--r--Doc/library/copy.rst85
1 files changed, 85 insertions, 0 deletions
diff --git a/Doc/library/copy.rst b/Doc/library/copy.rst
new file mode 100644
index 0000000000..6fb3100679
--- /dev/null
+++ b/Doc/library/copy.rst
@@ -0,0 +1,85 @@
+
+:mod:`copy` --- Shallow and deep copy operations
+================================================
+
+.. module:: copy
+ :synopsis: Shallow and deep copy operations.
+
+
+.. index::
+ single: copy() (in copy)
+ single: deepcopy() (in copy)
+
+This module provides generic (shallow and deep) copying operations.
+
+Interface summary::
+
+ import copy
+
+ x = copy.copy(y) # make a shallow copy of y
+ x = copy.deepcopy(y) # make a deep copy of y
+
+For module specific errors, :exc:`copy.error` is raised.
+
+.. %
+
+The difference between shallow and deep copying is only relevant for compound
+objects (objects that contain other objects, like lists or class instances):
+
+* A *shallow copy* constructs a new compound object and then (to the extent
+ possible) inserts *references* into it to the objects found in the original.
+
+* A *deep copy* constructs a new compound object and then, recursively, inserts
+ *copies* into it of the objects found in the original.
+
+Two problems often exist with deep copy operations that don't exist with shallow
+copy operations:
+
+* Recursive objects (compound objects that, directly or indirectly, contain a
+ reference to themselves) may cause a recursive loop.
+
+* Because deep copy copies *everything* it may copy too much, e.g.,
+ administrative data structures that should be shared even between copies.
+
+The :func:`deepcopy` function avoids these problems by:
+
+* keeping a "memo" dictionary of objects already copied during the current
+ copying pass; and
+
+* letting user-defined classes override the copying operation or the set of
+ components copied.
+
+This module does not copy types like module, method, stack trace, stack frame,
+file, socket, window, array, or any similar types. It does "copy" functions and
+classes (shallow and deeply), by returning the original object unchanged; this
+is compatible with the way these are treated by the :mod:`pickle` module.
+
+.. versionchanged:: 2.5
+ Added copying functions.
+
+.. index:: module: pickle
+
+Classes can use the same interfaces to control copying that they use to control
+pickling. See the description of module :mod:`pickle` for information on these
+methods. The :mod:`copy` module does not use the :mod:`copy_reg` registration
+module.
+
+.. index::
+ single: __copy__() (copy protocol)
+ single: __deepcopy__() (copy protocol)
+
+In order for a class to define its own copy implementation, it can define
+special methods :meth:`__copy__` and :meth:`__deepcopy__`. The former is called
+to implement the shallow copy operation; no additional arguments are passed.
+The latter is called to implement the deep copy operation; it is passed one
+argument, the memo dictionary. If the :meth:`__deepcopy__` implementation needs
+to make a deep copy of a component, it should call the :func:`deepcopy` function
+with the component as first argument and the memo dictionary as second argument.
+
+
+.. seealso::
+
+ Module :mod:`pickle`
+ Discussion of the special methods used to support object state retrieval and
+ restoration.
+