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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Backslash in f-string format specifier gets escape","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\nBetween Python 3.12 alpha 7 and beta 1 the behaviour of format specifiers containing a backslash (e.g. `\\n`, `\\u2603`) in f-strings changed.\r\n\r\nPreviously, the `__format__` method would get e.g. the newline character, but it now receives a backslash and an `n` character (i.e. the string `\"\\n\"`)\r\n\r\nThe following script demonstrates this:\r\n\r\n```python3\r\n# issue.py\r\n\r\nclass F:\r\n\tdef __format__(self, format_spec):\r\n\t\tprint(\"spec:\", repr(format_spec))\r\n\t\treturn format_spec.join([\"a\", \"b\", \"c\"])\r\n\r\nprint(\"out: \", repr((f\"{F():\\n}\")))\r\nprint(\"out: \", repr((f\"{F():\\u2603}\")))\r\n\r\nprint(\"out: \", repr((format(F(), \"\\n\"))))\r\nprint(\"out: \", repr((format(F(), \"\\u2603\"))))\r\n```\r\n\r\n```console\r\n$ python3.11 issue.py\r\nspec: '\\n'\r\nout:  'a\\nb\\nc'\r\nspec: '☃'\r\nout:  'a☃b☃c'\r\nspec: '\\n'\r\nout:  'a\\nb\\nc'\r\nspec: '☃'\r\nout:  'a☃b☃c'\r\n```\r\n\r\n\r\n```console\r\n$ python3.12 issue.py\r\nspec: '\\\\n'\r\nout:  'a\\\\nb\\\\nc'\r\nspec: '\\\\u2603'\r\nout:  'a\\\\u2603b\\\\u2603c'\r\nspec: '\\n'\r\nout:  'a\\nb\\nc'\r\nspec: '☃'\r\nout:  'a☃b☃c'\r\n```\r\n\r\nIn both cases the `format()` function works correctly - I only encounter the issue with f-strings.\r\n\r\nI suspect this is related to the PEP 701 changes to f-strings, but I couldn't find anything in the discussion of that PEP to suggest this was a deliberate change.\r\n\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 3.11.2, 3.12.0alpha7, 3.12.0beta1\r\n- Operating system and architecture: Ubuntu 20.04 (AMD64)\r\n\r\n\u003c!--\r\nYou can freely edit this text. Remove any lines you believe are unnecessary.\r\n--\u003e\r\n\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-105231\n* gh-105234\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/domdfcoding","@type":"Person","name":"domdfcoding"},"datePublished":"2023-06-01T13:07:09.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/105194/cpython/issues/105194"}