> Can you flesh this out for what stumbled into being my running example? That is, how could a regexp pattern object be part of a cycle?
Let me try to remember when we saw this problem in the past, but on first sigh, it seems that indeed that cannot happen in the regular case. > And, in general, I can't add attributes to p, or change their bindings: That's after the changes to add a new Py_TPFLAGS_IMMUTABLETYPE flag, which predates the creation of the issue we are discussing. But in general, new heap types are not immutable by default (check https://bugs.python.org/issue43908). For instance, in python3.8: >>> array.array.x = 4 Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: can't set attributes of built-in/extension type 'array.array' but in python 3.10.0a7 (before Py_TPFLAGS_IMMUTABLETYPE): Python 3.10.0a7 (tags/v3.10.0a7:53e55290cf, May 27 2021, 20:20:26) [Clang 12.0.0 (clang-1200.0.32.29)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import array >>> instance = array.array("f") >>> type = array.array >>> type.instance = instance On Thu, 27 May 2021 at 20:15, Tim Peters <tim.pet...@gmail.com> wrote: > [Tim] > >> And if a type pointer is the only thing being visited, then there's no > point > >> unless the object can itself be reachable from the type object. > > {Pablo] > > But that could happen easily for heap types as they are mutable by > > default. For instance, you set the instance in a global: > > > > type -> module -> globals -> instance -> type > > Sorry, but this is apparently a rat's nest and that's too sketchy for me > ;-) > > Can you flesh this out for what stumbled into being my running > example? That is, how could a regexp pattern object be part of a > cycle? > > >>> import re > >>> p = re.compile("ab*c") > >>> type(p) > <class 're.Pattern'> > >>> type(p).__module__ > 're' > >>> type(type(p).__module__) > <class 'str'> > > That is, its __module__ attribute is a string, not a module object. > > And, in general, I can't add attributes to p, or change their bindings: > > >>> p.flags > 32 > >>> p.flags = re > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > AttributeError: readonly attribute > >>> p.newattr = re > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > AttributeError: 're.Pattern' object has no attribute 'newattr' > > I just don't see a way to trick it into being part of a cycle. > > Not denying that safe is better than sorry, though. >
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