Circular references and python
Martin von Loewis
loewis at informatik.hu-berlin.de
Wed Feb 2 17:06:58 EST 2000
"Brian Dam Pedersen" <brian.pedersen at mail.danbbs.dk> writes:
> Now the lists are circular referenced, and dereferencing them will
> not garbage-collect them. To break up the chain just do
The essential piece here is that you have to break the circularity
with explicit code; Python will then clean-up the rest when you drop
the last reference to the structure.
Since cyclic structures are usually regular in some way, it is often
easy to break the cycles with a recursive algorithm. Consider
self.prev,self.next = prev,next
This could be used in a double-linked list (not that a double-linked
list is particular useful in Python :-). To allow breaking the cycles,
you can do
self.next=None # or self.prev=None
If you know you don't need such a list (stored in a variable head)
anymore, you do
and it will remove everything.
So it is very easy to deal with the problem when you know what it is.
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