René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"False positive for lambda within a function","articleBody":"**Related Bug**\r\n\r\nCould be a duplicate of:\r\n- https://github.com/python/mypy/issues/4297\r\n\r\n**Bug Report**\r\n\r\nWhen running mypy with a function returning an Optional the contains of a lambda expression is interpreted as optional and a type error is raised\r\n\r\n**To Reproduce**\r\n\r\nRun `mypy` against the following file:\r\n\r\n```python3\r\nfrom typing import Optional\r\n\r\nanimals = [\"cow\"]\r\n\r\n\r\ndef find1(name: str) -\u003e Optional[str]:\r\n    return next(\r\n        filter(\r\n            lambda animal: animal.upper() == name,\r\n            animals,\r\n        ),\r\n        None,\r\n    )\r\n```\r\n\r\n**Expected Behavior**\r\n\r\nNo type errors should be returned\r\n\r\n**Actual Behavior**\r\n\r\n```shell\r\n$ mypy bug.py\r\nbug.py:9: error: Item \"None\" of \"Optional[str]\" has no attribute \"upper\"\r\n```\r\n\r\nNOTE: Same error with returning \"Union[str, None]\"\r\nNOTE: Removing the Optional[str] stops the error, but that defaults the point \r\n\r\n```python3\r\ndef find1(name: str):\r\n    return next(\r\n        filter(\r\n            lambda animal: animal.upper() == name,\r\n            animals,\r\n        ),\r\n        None,\r\n    )\r\n```\r\n\r\n**Your Environment**\r\n\r\n- Mypy version used: 0.812\r\n- Mypy command-line flags: None\r\n- Mypy configuration options from `mypy.ini` (and other config files): None\r\n- Python version used: 3.9.4\r\n- Operating system and version: MacOS 10.15.7\r\n","author":{"url":"https://github.com/michaelbrewer","@type":"Person","name":"michaelbrewer"},"datePublished":"2021-05-06T04:03:44.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/10426/mypy/issues/10426"}