Benjamin Kaplan wrote:
You're still misunderstanding Python's object model. del does NOT
delete an object. It deletes a name. The only way for an object to be
deleted is for it to be inaccessible (there are no references to it,
or there are no reachable references to it).
foo = object()
bar = foo
foo
<object object at 0x01CE14C0>
bar
<object object at 0x01CE14C0>
del foo
bar
<object object at 0x01CE14C0>
foo
Traceback (most recent call last):
File "<pyshell#7>", line 1, in <module>
foo
NameError: name 'foo' is not defined
There is no way to force the go_to_heaven method to delete the head
unless you can make sure that all other references to the head are
weak references. If you need strictly-enforced relationships, Python
is probably not the right language for the job- you'll be better off
with C++ or Java.
Having said all that, you could do something like:
class BodyPart(object):
_alive = True
def __nonzero__(self):
return self._alive
def die(self):
self._alive = False
class Head(BodyPart):
"will contain things like Brain, Eyes, etc"
size = 5
class Body(BodyPart):
def __init__(self):
self._head = Head()
def go_to_heaven(self):
self._head.die()
self.die()
John_Doe = Body()
if John_Doe:
print "John Doe is alive!"
John_Doe.go_to_heaven()
if John_Doe:
print "uh oh - something wrong"
else:
print "John Doe is no longer with us"
print "and his head is %s" % ('alive' if John_Doe._head else 'dead')
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