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, 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 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 pickle module.
Changed in version 2.5:
Added copying functions.
Classes can use the same interfaces to control copying that they use
to control pickling. See the description of module
pickle for information on these
methods. The copy module does not use the
copy_reg registration module.
In order for a class to define its own copy implementation, it can
define special methods __copy__() and
__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 __deepcopy__()
implementation needs to make a deep copy of a component, it should
call the deepcopy() function with the component as first
argument and the memo dictionary as second argument.
