René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"False positive with --warn-unreachable when an instance variable is modified inside a for loop","articleBody":"**Bug Report**\r\n\r\nmypy mark as unreachable code that is perfectly reachable, perhaps because it interprets an instance variable typed as Optional to always be None.\r\n\r\n**To Reproduce**\r\n\r\n```python\r\n\r\n\r\nfrom typing import Optional\r\n\r\n# executed with --warn-unreachable\r\n\r\nclass A:\r\n    x: Optional[int]\r\n\r\n    def execute(self) -\u003e None:\r\n        self.x = None\r\n        for i in range(3):\r\n            if self.x is None:\r\n                self.x = 10\r\n            else:\r\n                self.x = 20  # error: Statement is unreachable  [unreachable]\r\n            print(self.x)\r\n\r\n\r\na = A()\r\na.execute()\r\n```\r\n\r\n[Gist](https://gist.github.com/mypy-play/c4a0b051484c30474289868dd9ceb8e5)\r\n[Playground URL](https://mypy-play.net/?mypy=latest\u0026python=3.10\u0026flags=warn-unreachable\u0026gist=c4a0b051484c30474289868dd9ceb8e5)\r\n\r\n**Expected Behavior**\r\n\r\nNo errors.\r\n\r\n**Actual Behavior**\r\n\r\nShowing: `error: Statement is unreachable  [unreachable]`\r\n\r\n**Your Environment**\r\n\r\n- Mypy version used: 0.982\r\n- Mypy command-line flags: --warn-unreachable\r\n- Mypy configuration options from `mypy.ini` (and other config files):\r\n- Python version used: 3.10\r\n\r\n","author":{"url":"https://github.com/autosquash","@type":"Person","name":"autosquash"},"datePublished":"2022-10-31T13:02:38.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/13973/mypy/issues/13973"}