[Tutor] classes and the deepcopy function

Tiger12506 keridee at jayco.net
Mon Jan 7 23:23:12 CET 2008

> Hi
> I was trying to learn about classes in Python and have been playing
> around but I am having a problem with the deepcopy function. I want to
> have a function that returns a clean copy of an object that you can
> change without it changing the original, but no matter what I do the
> original changes as well. Can anyone give ma a pointer?

What's really cute about this is the underlying pointers to PyObject s 
giving you troubles. ;-) So you see, you have lots of pointers!

> def move_rectangle(rect, dx, dy):
>    rect2 = copy.deepcopy(rect)
>    rect2.corner.x += dx
>    rect2.corner.y += dy
>    return rect2

I want to mention something, even though the whole discussion has been 
beneficial to me as well as to others I'm sure, that you don't need a 
deepcopy here at all. I know that perhaps this is a simplified version of 
code that you might be working on, but perhaps the full version can be 
adapted as well???

def move_rectangle(rect, dx, dy):
  rect2 = rectange()
  rect2.width = rect.width
  rect2.height = rect.height
  rect2.corner.x = rect.corner.x+dx
  rect2.corner.y = rect.corner.y+dy
  return rect2

Hmmm... perhaps the necessary but cumbersome width and the height 
assignments are what makes the deepcopy so helpful in this example... 
Certainly they foreshadow the application of a lot of work with similar 
examples and larger objects....


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