On 11/12/19 7:47 am, R.Wieser wrote:
what happens when the reference becomes zero: is the __del__ method called directly (as I find logical), or is it only called when the garbage collector actually removes the instance from memory (which Chris thinks what happens) ?
In CPython, these are the same thing. As soon as the reference count becomes zero, the __del__ method is called *and* the object is removed from memory. This remains true even in the presence of reference cycles. As long as the object is part of a cycle, it's reference count is not zero. When the cyclic garbage collector gets around to noticing the cycle, it breaks it, causing the reference counts of the objects in it to become zero, in turn causing them to be collected. In a Python implementation that doesn't use reference counts, using "del" on the last reference to an object probably isn't going to do anything to the object. You seem to think it would be logical for it to call the __del__ method there and then, instead of waiting until the object is collected. But without reference counting, it has no way of *knowing* that it's the last reference until the garbage collector does its thing. To summarise, your logic on this point is flawed.
As a simple bit of testcode has shown me (read my reply to Chris).
We're not saying that your code won't work -- in current CPython it will. We're saying that it relies on an implementation detail. To demonstrate that with a code example, it would have to be run on a different implementation of Python that didn't use reference counting, such as Jython. -- Greg -- https://mail.python.org/mailman/listinfo/python-list
