{
  "id": 6017436,
  "title": "My safety check was an assert. Five lines made the module refuse to load without it.",
  "url": "https://urgent.news/2026/09/06/my-safety-check-was-an-assert-five-lines-made-the-module-refuse-to",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-09-06T18:50:12.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/mahirhir/my-safety-check-was-an-assert-five-lines-made-the-module-refuse-to-load-without-it-36n3"
  },
  "original_language": "en",
  "account": "The safety check implemented by five lines of code in a module resolves the issue where the module would refuse to load when executed with the optimization flag -O. This safety measure ensures that the module cannot be imported in a mode where its checks are essentially ignored. By raising a RuntimeError, the module refuses to run when executed with -O, preventing any potential problems that might arise due to the safety checks being disabled. This approach addresses two different questions: the question of which image the module was imported under, and the question of what process is running at the moment. The safety check leverages the sys.flags.optimize setting and the __debug__ variable to determine the correct behavior. By using this method, the module ensures that it is safe to run under -O and avoids any unexpected behavior or issues that may arise from relying solely on asserts.",
  "summary": "assert isinstance(flag, bool) reads like a check. Under python -O it is not there at all, and nothing at the call site says so. The usual advice is to stop writing safety checks as asserts. There is a better answer: let the module refuse to be imported in the mode where its checks evaporate. if not __debug__ : raise RuntimeError ( \" this module ' s checks are asserts; refusing to run with -O \" )…",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}