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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"\"RuntimeWarning: assigning None to unbound local\": an inscrutable error","articleBody":"# Documentation\r\n\r\n`RuntimeWarning: assigning None to unbound local` ← I get this periodically since upgrading to python 3.12, for various lines of library code somewhere deep in my project's dependencies, and it seems like there's no documentation for it online? It's not even clear to me from the error message why this would be a bad thing to happen. These warnings generally seem to show up in list comprehensions. I don't know how to fix them or what they indicate. Maybe it's even a bug in python! I'm using Python 3.12.6 on Windows 10.\r\n\r\nHere's an example from today:\r\n\r\n```python\r\nC:\\[...]\\.venv\\Lib\\site-packages\\asttokens\\util.py:173: RuntimeWarning: assigning None to unbound local 'n'\r\n  if isinstance(c, type) and issubclass(c, ast.expr)} |\r\nC:\\[...]\\.venv\\Lib\\site-packages\\asttokens\\util.py:173: RuntimeWarning: assigning None to unbound local 'c'\r\n  if isinstance(c, type) and issubclass(c, ast.expr)} |\r\n  ```\r\n\r\nHere's the line it's complaining about: https://github.com/gristlabs/asttokens/blob/2ff0e8d157fa89c22fe16839ab060b33f4c888bd/asttokens/util.py#L173\r\n\r\nHere's another:\r\n```python\r\nC:\\[...]\\.venv\\Lib\\site-packages\\scipy\\sparse\\__init__.py:315: RuntimeWarning: assigning None to unbound local 's'\r\n  __all__ = [s for s in dir() if not s.startswith('_')]\r\n```","author":{"url":"https://github.com/wyattscarpenter","@type":"Person","name":"wyattscarpenter"},"datePublished":"2024-09-16T10:26:09.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":12},"url":"https://github.com/124118/cpython/issues/124118"}