10000 gh-135552: Add tests that check if weakref for tp_subclasses cleared after finalization by sergey-miryanov · Pull Request #136304 · python/cpython · GitHub
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gh-135552: Add tests that check if weakref for tp_subclasses cleared after finalization #136304

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gh-135552: Add tests that check if weakref for tp_subclasses cleared after finalization #136304

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@sergey-miryanov sergey-miryanov commented Jul 4, 2025 •
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@bedevere-app bedevere-app bot added awaiting review tests Tests in the Lib/test dir labels Jul 4, 2025
@bedevere-app bedevere-app bot mentioned this pull request Jul 4, 2025
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@sergey-miryanov
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I believe this PR should skip news

neonene
neonene reviewed Jul 4, 2025
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nascheme commented Jul 8, 2025

This looks okay to me. Some suggested improvements. The new test might fit better into test_weakref.py but that's minor.

I don't think it's required to run these in a separate Python process. That makes the test run slower and it's not supposed to crash. Generally a separate process is used for the tests that exercise the interpreter shutdown logic and we are not testing that. So you could just do:

    def test_clearing_weakrefs_in_gc(self):
        # This test checks that:
        # 1. weakrefs for types with callbacks are cleared before the
        # finalizer is called
        # 2. weakrefs for types without callbacks are cleared after the
        # finalizer is called
        # 3. other weakrefs cleared before the finalizer is called
        errors = []
        class Class:
            def __init__(self):
                self._self = self
                self._1 = weakref.ref(Class, lambda x: None)
                self._2 = weakref.ref(Class)
                self._3 = weakref.ref(self)

            def __del__(self):
                if self._1() is not None:
                    errors.append("Type weakref with callback is not None as expected")
                if self._2() is not Class:
                    errors.append("Type weakref is not Class as expected")
                if self._3() is not None:
                    errors.append("Instance weakref is not None as expected")
        Class()
        gc.collect()
        self.assertEqual(errors, [])

I find the variable naming a bit esoteric. I would have just called them wr1, wr2 and wr3.

@sergey-miryanov
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@nascheme Thanks for review! Fixed.

kumaraditya303
kumaraditya303 reviewed Jul 8, 2025
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kumaraditya303
kumaraditya303 reviewed Jul 8, 2025
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7788e55 
Co-authored-by: Kumar Aditya <kumaraditya@python.org>
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@kumaraditya303 Thanks for review!

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