is it a bug in Module copy or i am wrong??
python version 2.5 in module copy we all know that copy have two method: copy() and deepcopy(). and the explain is - A shallow copy constructs a new compound object and then (to the extent possible) inserts *the same objects* into it that the original contains. - A deep copy constructs a new compound object and then, recursively, inserts *copies* into it of the objects found in the original. so i try a example: import copy class A: i = 1 class B: a = A() b = B() x=copy.copy(b) y=copy.deepcopy(b) print id(x.a), id(b.a) print id(y.a), id(y.a) the result: 14505264 14505264 14505264 14505264 So maybe i have a wrong understand to deep copy and shallow copy or it is a bug ? please help me!! -- http://mail.python.org/mailman/listinfo/python-list
Re: is it a bug in Module copy or i am wrong??
On Thu, Nov 6, 2008 at 11:59 PM, yoma [EMAIL PROTECTED] wrote: python version 2.5 in module copy we all know that copy have two method: copy() and deepcopy(). and the explain is - A shallow copy constructs a new compound object and then (to the extent possible) inserts *the same objects* into it that the original contains. - A deep copy constructs a new compound object and then, recursively, inserts *copies* into it of the objects found in the original. so i try a example: import copy class A: i = 1 class B: a = A() Note that `a` is a class variable, not an instance variable. This ends up being important. b = B() x=copy.copy(b) y=copy.deepcopy(b) I believe these only copy the instance variables of `b`. They do NOT copy the class `B` (IMHO, copying B would be weird and unexpected behavior here anyway) or its constituent variables, such as `a`. print id(x.a), id(b.a) print id(y.a), id(y.a) the result: 14505264 14505264 14505264 14505264 Thus this makes sense. These all refer to B's variable `a`, which is a class variable and therefore not copied by copy() or deepcopy()-ing `b`, an *instance* of class B. The fact that you can access `a` through B instances does not mean that `a` belongs to any instance of B and is merely a result of how Python's object system works. Disclaimer: I am not a CPython dev and did not look at the `copy` module's sources. Cheers, Chris -- Follow the path of the Iguana... http://rebertia.com So maybe i have a wrong understand to deep copy and shallow copy or it is a bug ? please help me!! -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: is it a bug in Module copy or i am wrong??
On Thu, 06 Nov 2008 23:59:51 -0800, yoma wrote: import copy class A: i = 1 class B: a = A() b = B() x=copy.copy(b) y=copy.deepcopy(b) print id(x.a), id(b.a) print id(y.a), id(y.a) the result: 14505264 14505264 14505264 14505264 So maybe i have a wrong understand to deep copy and shallow copy or it is a bug ? Additionally to Chris' explanation: You will get the same `id()` for every copy of a 1 in CPython. Numbers are immutable so the CPython implementation caches small integers as an optimization. Ciao, Marc 'BlackJack' Rintsch -- http://mail.python.org/mailman/listinfo/python-list
Re: is it a bug in Module copy or i am wrong??
yoma wrote: python version 2.5 in module copy we all know that copy have two method: copy() and deepcopy(). and the explain is - A shallow copy constructs a new compound object and then (to the extent possible) inserts *the same objects* into it that the original contains. - A deep copy constructs a new compound object and then, recursively, inserts *copies* into it of the objects found in the original. Read a little further: 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 so i try a example: import copy class A: i = 1 class B: a = A() b = B() The only attribute of b itself is .__class__ == B, which as the above says, is 'copied' by not being copied. So either shallow or deep copies of b will have .__class__ == the original B with its original instance of a. tjr -- http://mail.python.org/mailman/listinfo/python-list
