The super() __init__ function fills in the fields of a super object without checking if they were already set.  If someone happens to call __init__ again, the previously-set references will end up getting forgotten and leak memory.

For example:

import sys
print(sys.gettotalrefcount())
sp = super(int, 1)
for i in range(100000):
  super.__init__(sp, float, 1.0)
print(sys.gettotalrefcount())

If super used __new__ instead of __init__, this issue probably wouldn't arise.

I'm surprised that super is subclassable.

Any uses of super() beyond the documented idioms are uninteresting, except they should not be usable as crash or DoS vectors.

Based on Guido's feedback and the fact that this isn't documented usage of super() and hence no promises to not re-initialize, I'm closing as "not a bug". Sorry, Kevin.

Actually, the refcount bug is still a bug.

Possible solutions:

1. Correctly decref old values.
2. Raise an exception if super.__init__ is caled multiple times.
3. Remove super.__init__ and add super.__new__.

What is more preferable?

Do #1.

--Guido (mobile)
On Apr 11, 2016 11:31 PM, "Serhiy Storchaka" <report@bugs.python.org> wrote:

>
> Serhiy Storchaka added the comment:
>
> Possible solutions:
>
> 1. Correctly decref old values.
> 2. Raise an exception if super.__init__ is caled multiple times.
> 3. Remove super.__init__ and add super.__new__.
>
> What is more preferable?
>
> ----------
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue26718>
> _______________________________________
>

Here is a patch.

super_init_leaks.patch LGTM, it fixes. I confirm that the patch fixes the refleak. I checked with:

$ ./python -m test -R 3:3 test_super

Added more comments as suggested by Guido.

super_init_leaks_2.patch LGTM.

New changeset 450f36750cb9 by Serhiy Storchaka in branch '3.5':
Issue #26718: super.__init__ no longer leaks memory if called multiple times.
https://hg.python.org/cpython/rev/450f36750cb9

New changeset 4680438f486f by Serhiy Storchaka in branch '2.7':
Issue #26718: super.__init__ no longer leaks memory if called multiple times.
https://hg.python.org/cpython/rev/4680438f486f

New changeset 55f4c1f8ca6a by Serhiy Storchaka in branch 'default':
Issue #26718: super.__init__ no longer leaks memory if called multiple times.
https://hg.python.org/cpython/rev/55f4c1f8ca6a