René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"str.maketrans on a mutating dict is not thread-safe","articleBody":"# Crash report\n\n### What happened?\n\nA reproducer (in the format of `Lib/tests/test_free_threading/xxx.py`):\n\n```python\nimport unittest\nfrom test.support import threading_helper\n\nthreading_helper.requires_working_threading(module=True)\n\n\nclass ItertoolsThreading(unittest.TestCase):\n\n    @threading_helper.reap_threads\n    def test_maketrans(self):\n        number_of_iterations = 10\n        number_of_attempts=100\n        for _ in range(number_of_iterations):\n            print(f'iteration {_}')\n            d = {2000: 'a'}\n            def work_iterator(dct):\n                for idx in range(number_of_attempts):\n                    str.maketrans(dct)\n                    idx = 2000 + idx # outside range of small ints\n                    dct[idx] = chr(idx%16)\n                    dct.pop(idx, None)\n            threading_helper.run_concurrently(work_iterator, nthreads=10, args=[d])\n\nif __name__ == \"__main__\":\n    unittest.main()\n    print('done')\n```\n\nAt first glance it seems that the iteration using `PyDict_Next` is not safe (but maybe there are more unsafe parts):\n\nhttps://github.com/python/cpython/blob/24cc998c164f137603f1c6d95b929d640211d237/Objects/unicodeobject.c#L13158\n\n\n(found when reviewing #145129)\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nWindows\n\n### Output from running 'python -VV' on the command line:\n\n_No response_\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-145157\n* gh-145320\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/eendebakpt","@type":"Person","name":"eendebakpt"},"datePublished":"2026-02-23T14:33:24.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/145142/cpython/issues/145142"}