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| '''`copy`''' is a module for deep- and shallow-copying operations. | '''`copy`''' is a module for deep- and shallow-copying operations. This is useful for any objects that are passed by reference, especially lists. |
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| === Copy === | Two functions are exposed: '''`copy()`''' and '''`deepcopy()`'''. |
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| Make a shallow copy of an object. | To create a deep copy, try: |
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| {{{ import copy |
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| class foo(object): def __init__(self, name): self.name = name |
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| === DeepCopy === | def __eq__(self, other): return self.name == other.name |
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| Make a deep copy of an object. | a = foo("foo") lista = [a] listb = lista lista[0] == listb[0] # True lista[0] is listb[0] # True listc = copy.deepcopy(lista) lista[0] == listc[0] # True lista[0] is listc[0] # False }}} |
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| [[https://pymotw.com/3/copy/|Python Module of the Week article for copy]] |
Python Copy
copy is a module for deep- and shallow-copying operations. This is useful for any objects that are passed by reference, especially lists.
Contents
Concept
A deep copy differs from a shallow copy only for containers. A shallow copy contains references to the same objects that the original contains. A deep copy contains copies of the original's contents.
This poses two challenges:
- Recursive objects may contain a reference to themselves, and causing a recursion loop
- Some data should be copied once and shared among the contents
Creating a deep copy then involves:
Allowing objects to override the operation to avoid loops; see __deepcopy__ for details
Keeping a memo dictionary for data already copied, so that it can be shared among the contents
Usage
Two functions are exposed: copy() and deepcopy().
To create a deep copy, try:
import copy
class foo(object):
def __init__(self, name):
self.name = name
def __eq__(self, other):
return self.name == other.name
a = foo("foo")
lista = [a]
listb = lista
lista[0] == listb[0] # True
lista[0] is listb[0] # True
listc = copy.deepcopy(lista)
lista[0] == listc[0] # True
lista[0] is listc[0] # False
See also
Python copy module documentation
Python Module of the Week article for copy