Michael Spencer wrote: > [EMAIL PROTECTED] wrote: [snip] > > Anyway, my present problem is that I want to make copies of instances > > of my own custom classes. I'm having a little trouble understanding > > the process. Not that I think that it matters -- but in case it does, > > I'll tell you that I'm running Python 2.3.4 on a Win32 machine. [snip] > If you google for: > python __deepcopy__ cookbook > you will find a couple of examples of this method in use, among them:
> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/259179 > > 1 class deque(object): > 2 > 3 def __init__(self, iterable=()): > 4 if not hasattr(self, 'data'): > 5 self.left = self.right = 0 > 6 self.data = {} > 7 self.extend(iterable) > > [...snip methods...] > > 8 def __deepcopy__(self, memo={}): > 9 from copy import deepcopy > 10 result = self.__class__() > 11 memo[id(self)] = result > 12 result.__init__(deepcopy(tuple(self), memo)) > 13 return result > > HTH > Michael Hi, Michael, I was indeed finding code like this in my web searches, though not this particular example. I'm glad that you cut out code that is irrelevant to the deepcopy operation. Still, I want to understand what is going on here, and I don't. I've numbered the lines in your example. So, entering deepcopy, I encounter the first new concept (for me) on line 10. We obtain the class/type of self. On line 11 we create a dictionary item in memo, [id(self):type(self)]. So now I'm confused as to the purpose of memo. Why should it contain the ID of the *original* object? Things get even stranger for me on line 12. Working from the inside of the parentheses outward, an attempt is made to convert self to a tuple. Shouldn't this generate a TypeError when given a complex, non-iterable item like the deque class? I just tried running one of my programs, which assigns the name "x" to one of my custom objects, and when I execute tuple(x), a TypeError is what I get. Anyway, I like what I think I see when you finally call __init__ for the copied object, on lines 4-6. If __deepcopy__ calls __init__, then the new deque object should already have a "data" attribute. So "data" is only initialized if it doesn't already exist. I do not understand whether the "iterable" variable, which appears on lines 3 and 7, is relevant to the copying operation. Line 12 calls __init__ with a single argument, not two, so iterable should be declared as an empty tuple. Again I see what I think should generate a TypeError on line 7, when an attempt is made to extend the non-sequence object "self" with the iterable tuple. Is there another section of the Python docs that will clarify all this for me? I got hung up on all the "static", "public", etc. declarations in Java early on. Python has taken me an awful lot farther, but perhaps I'm hitting the conceptual wall again. -- Rainforest laid low. "Wake up and smell the ozone," Says man with chainsaw. John J. Ladasky Jr., Ph.D. -- http://mail.python.org/mailman/listinfo/python-list
