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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Argparse `add_argument` treats `-` in flags differently to `-` in positional arguments.","articleBody":"\u003c!--\r\n  If you're new to Python and you're not sure whether what you're experiencing is a bug, the CPython issue tracker is not\r\n  the right place to seek help. Consider the following options instead:\r\n\r\n  - reading the Python tutorial: https://docs.python.org/3/tutorial/\r\n  - posting in the \"Users\" category on discuss.python.org: https://discuss.python.org/c/users/7\r\n  - emailing the Python-list mailing list: https://mail.python.org/mailman/listinfo/python-list\r\n  - searching our issue tracker (https://github.com/python/cpython/issues) to see if\r\n    your problem has already been reported\r\n--\u003e\r\n\r\n**Bug report**\r\n\r\nIf you add an optional argument to a parser with `argparse` containing dashes,\r\nthose are converted to `_` automatically in the resulting Namespace object.\r\n\r\nBut if you add a positional argument containing a `-`, this is not converted and the resulting error message suggests the argument name containing the `-` instead of the `_`. Which is of course not possible (without `getattr`), because it's not a valid variable name in Python.\r\n\r\nThis behaviour is misleading and undocumented and I'd suggest to convert `-` to `_` in positional arguments too.\r\n\r\nReproduction code:\r\n```python\r\nimport argparse\r\n\r\nparser = argparse.ArgumentParser(\"example\")\r\n\r\nparser.add_argument(\"foo-bar\", type=str)\r\n\r\nargs = parser.parse_args()\r\n\r\nprint(\"getattr\", getattr(args, \"foo-bar\"))\r\n\r\nprint(\"- replaced by _\", args.foo_bar)\r\n\r\n```\r\n\r\nResults in:\r\n```bash\r\n$ python3 main.py abc\r\ngetattr aoe\r\nTraceback (most recent call last):\r\n  File \"/tmp/main.py\", line 11, in \u003cmodule\u003e\r\n    print(\"- replaced by _\", args.foo_bar)\r\nAttributeError: 'Namespace' object has no attribute 'foo_bar'. Did you mean: 'foo-bar'?\r\n\r\n```\r\n\r\nCompounding this issue is the fact, that you are prevented from using the `dest` option on `add_argument` to overwrite the name in the Namespace.\r\n\r\n**Your environment**\r\n\r\n\u003c!-- Include as many relevant details as possible about the environment you experienced the bug in --\u003e\r\n\r\n- CPython versions tested on: Python 3.10.5\r\n- Operating system and architecture: Linux\r\n\r\n\u003c!--\r\nYou can freely edit this text. Remove any lines you believe are unnecessary.\r\n--\u003e\r\n","author":{"url":"https://github.com/CSDUMMI","@type":"Person","name":"CSDUMMI"},"datePublished":"2022-07-21T18:02:13.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":24},"url":"https://github.com/95100/cpython/issues/95100"}