Deeper copy than deepcopy

[Gary Herron]

Scott Pakin wrote:
> copy.deepcopy apparently preserves multiple references to the same object:
>
>     $ python
>     Python 2.5.2 (r252:60911, Jan  4 2009, 17:40:26)
>     [GCC 4.3.2] on linux2
>     Type "help", "copyright", "credits" or "license" for more information.
>     >>> import copy
>     >>> d = [1,2,3]
>     >>> r = copy.deepcopy([d]*3)
>     >>> r
>     [[1, 2, 3], [1, 2, 3], [1, 2, 3]]
>     >>> r[1][2] = 999
>     >>> d
>     [1, 2, 3]
>     >>> r
>     [[1, 2, 999], [1, 2, 999], [1, 2, 999]]
>     >>>
>
> I wanted to wind up with r being [[1, 2, 3], [1, 2, 999], [1, 2, 3]].
> What's the right way to construct r as a list of *independent* d lists?
>
> Thanks,
> -- Scott
>   

Try this:

 >>>
 >>> d = [1,2,3]
 >>> r = [[x for x in d] for i in range(3)]
 >>> r[1][2] = 999
 >>> r
[[1, 2, 3], [1, 2, 999], [1, 2, 3]]

Gary Herron