copy.deepcopy( ) vs copy.copy( )

[Fousi sadath]

i want to know about the copy.deecopy( ) function in python

[bartonc]

i want to know about the copy.deecopy( ) function in python

deepcopy() is for making copies of iterables which may contain iterables. This is as compared to copy() that makes "shallow" copies of (say) lists that are inside a list. To understand the difference, you need to get the whole "pass by reference" thing. I'll try to illustrate:

>>> listA = ['spam', 'spam', 'spam', 'spam',]
>>> listB = listA    # a reference (not a new object)
>>> listB[-1] = 'eggs'
>>> print listA
['spam', 'spam', 'spam', 'eggs']
>>> import copy
>>> listC = copy.copy(listA)    # create a new object
>>> listC[-1] = 'toast'
>>> print listA
['spam', 'spam', 'spam', 'eggs']
>>> print listC
['spam', 'spam', 'spam', 'toast']
>>> listABC =[listA, listB, listC]
>>> listDEF = listABC    # copy.copy() would also give a list of references (not new objects)
>>> listDEF[0][-1] = 'jelly' # last element of listA
>>> print listA
['spam', 'spam', 'spam', 'jelly']
>>> listXYZ = copy.deepcopy(listABC)  # create a list of new objects
>>> listXYZ[0][-1] = 'spam' # NOT the last element of listA
>>> print listA
['spam', 'spam', 'spam', 'jelly']
>>> 

[bartonc]

deepcopy() is for making copies of iterables which may contain iterables. This is as compared to copy() that makes "shallow" copies of (say) lists that are inside a list. To understand the difference, you need to get the whole "pass by reference" thing. I'll try to illustrate:

>>> listA = ['spam', 'spam', 'spam', 'spam',]
>>> listB = listA    # a reference (not a new object)
>>> listB[-1] = 'eggs'
>>> print listA
['spam', 'spam', 'spam', 'eggs']
>>> import copy
>>> listC = copy.copy(listA)    # create a new object
>>> listC[-1] = 'toast'
>>> print listA
['spam', 'spam', 'spam', 'eggs']
>>> print listC
['spam', 'spam', 'spam', 'toast']
>>> listABC =[listA, listB, listC]
>>> listDEF = listABC    # copy.copy() would also give a list of references (not new objects)
>>> listDEF[0][-1] = 'jelly' # last element of listA
>>> print listA
['spam', 'spam', 'spam', 'jelly']
>>> listXYZ = copy.deepcopy(listABC)  # create a list of new objects
>>> listXYZ[0][-1] = 'spam' # NOT the last element of listA
>>> print listA
['spam', 'spam', 'spam', 'jelly']
>>> 

I just had to prove to myself that I knew what I was saying was true:

['spam', 'spam', 'spam', 'jelly']
>>> listDEF = copy.copy(listABC)
>>> listDEF[0][-1] = 'spam' # last element of listA
>>> print listA
['spam', 'spam', 'spam', 'spam']
>>>