[Jython-dev] Re: Question about copied objects...

[<bc...@wo...>]

[Rich Seddon on jython-users]

>We're seeing some behavior with the copy module in 
>Jython.
>
>In the following test program, __del__ is only called 
>for for the original objects, never for the copied 
>ones.
>
>Is this normal? 

Nah, it's a bug.

>The same program (without java calls,
>of course) for CPython shows __del__ being called for
>both the original and copied objects.

The problem occur because __del__ is only called when it is defined in
the class dict at the time the class is created. This is slightly more
restrictive than CPython where a __del__ attribute can be added at any
time.

When using copy.copy() & copy.deepcopy(), the new instance is first
created as an empty dummy class and only later is the correct class
assigned to the instance. Because the empty dummy class didn't define a
__del__ method, the method will not be called even when a __del__ method
is acquired later.

The patch below should be usefull as a workaround.

regards,
finn


--- I:\Python21\Lib\copy.py     Sat Jan 20 16:47:18 2001
+++ i:\java\jython.CVS\Lib\copy.py      Fri Jun 01 10:04:43 2001
@@ -121,7 +121,10 @@
         args = x.__getinitargs__()
         y = apply(x.__class__, args)
     else:
-        y = _EmptyClass()
+        if hasattr(x.__class__, '__del__'):
+            y = _EmptyClassDel()
+        else:
+            y = _EmptyClass()
         y.__class__ = x.__class__
     if hasattr(x, '__getstate__'):
         state = x.__getstate__()
@@ -237,7 +240,10 @@
         args = deepcopy(args, memo)
         y = apply(x.__class__, args)
     else:
-        y = _EmptyClass()
+        if hasattr(x.__class__, '__del__'):
+            y = _EmptyClassDel()
+        else:
+            y = _EmptyClass()
         y.__class__ = x.__class__
     memo[id(x)] = y
     if hasattr(x, '__getstate__'):
@@ -260,6 +266,12 @@
 # Helper for instance creation without calling __init__
 class _EmptyClass:
     pass
+
+# Helper for instance creation without calling __init__. Used when
+# the source class contains a __del__ attribute.
+class _EmptyClassDel:
+    def __del__(self):
+        pass

 def _test():
     l = [None, 1, 2L, 3.14, 'xyzzy', (1, 2L), [3.14, 'abc'],