There is a reference leak when using PyType_FromSpec with custom tp_dealloc.  This was first noted in issue #15142, where a fix was given which only applies to types which do not override tp_dealloc.

For example, the xxlimited.Xxo type suffers from this:

Python 3.3.0 (default, Oct 26 2012, 11:06:17) 
[GCC 4.6.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import xxlimited
>>> import sys
>>> Xxo = type(xxlimited.new())
>>> e = Xxo()
>>> sys.getrefcount(Xxo)
7
>>> e = Xxo()
>>> sys.getrefcount(Xxo)
8
>>> e = Xxo()
>>> sys.getrefcount(Xxo)
9

I see this issue came up in the course of #15653 as well.

The attached file `heaptype_refcnt_testcases.py` runs through several test cases (ssl.SSLError, a subclass of ssl.SSLError, and xxlimited.Xxo) seeing if references are leaked in each instance.

Unfortunately `xxlimited.Xxo` isn't set to be a base type and I don't know of any other types in the default install which use PyType_FromSpec with a custom tp_dealloc.

The new test cases for PEP 489 (multi-phase extension module import) appear to be encountering this leak.

See issue 24268 for context.

New changeset 265eeb60443a by Nick Coghlan in branch '3.5':
Issue #24373: Eliminate PEP 489 test refleaks
https://hg.python.org/cpython/rev/265eeb60443a