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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"missing global names inside a class body (calling `exec` with a `ChainMap`)","articleBody":"# Bug report\n\n### Bug description:\n\nI need to implement layered context running python code, so I choose `ChainMap`. But Python needs every `globals` passed to `exec` to be a `dict`, so I mixins it into `ChainMap`.\n\nThis patch runs well as far, but in a class it can't get the value from the outside.\n\nI think this may because in the class context CPython uses some function like `PyDict_Get` instead of `__getitem__`, so the values didn't get copied into the class's globals context.\n\nThis bug caused this code fails:\n\n```python\nfrom collections import ChainMap\n\nclass ChainMap(ChainMap, dict):  # globals must be a real dict\n    pass\n\nsource = \"\"\"\na = 1\n\nclass A:\n    print(a)\n\"\"\"\n\nexec(source, ChainMap())  # this line raises NameError\n```\n\n\u003cdetails\u003e\u003csummary\u003eOther reproduction approaches\u003c/summary\u003e\n\u003cp\u003e\n\nThis is reproduceable in [`pyodide`](https://github.com/pyodide/pyodide) (a wasm port of CPython 3.12.1), so you can run the code above by just clicking one of the following link:\n\n- [Stackblitz](https://stackblitz.com/edit/chainmap-class-locals-issue?file=main.py) - you can edit code and the result will sync instantly\n- [Python Online](https://pyth-on-line.vercel.app/console#ZnJvbSBjb2xsZWN0aW9ucyBpbXBvcnQgQ2hhaW5NYXAKCgpjbGFzcyBDaGFpbk1hcChDaGFpbk1hcCwgZGljdCk6ICAjIGdsb2JhbHMgbXVzdCBiZSBhIHJlYWwgZGljdAogICAgcGFzcwoKCnNvdXJjZSA9ICIiIgoKY2xhc3MgQToKICAgIHByaW50KGEpCgoiIiIKCgpleGVjKHNvdXJjZSwgeyJhIjogMX0pCgoKZXhlYyhzb3VyY2UsIENoYWluTWFwKHsiYSI6IDJ9KSkgICMgdGhpcyBsaW5lIHJhaXNlcyBlcnJvcgo=) - this is faster but just has a console instead of an IDE\n\n\u003c/p\u003e\n\u003c/details\u003e\n\n### CPython versions tested on:\n\n3.12\n\n### Operating systems tested on:\n\nLinux, Windows\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-121389\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/CNSeniorious000","@type":"Person","name":"CNSeniorious000"},"datePublished":"2024-07-03T06:59:48.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":19},"url":"https://github.com/121306/cpython/issues/121306"}