Python 'SyntaxError: f-string: expecting }' or 'f-string expression part cannot include a backslash' when reusing the same quotes (or nesting) inside an f-string. Works on 3.12 but fails on 3.11?

Cause: Before Python 3.12, f-strings were tokenized specially. The expression part could not contain the quote character that delimited the f-string, could not contain a backslash, could not hold a # comment, and had to stay on one line. Code like an f-string in double quotes that indexes a dict with double quotes inside the braces therefore fails with a SyntaxError (messages such as "f-string: expecting '}'" or "f-string expression part cannot include a backslash"). Python 3.12 adopted PEP 701, which parses f-strings with the normal grammar and removes those limits, so code written on 3.12+ often breaks on 3.11 and older. Fix (best first): 1. Make the code portable: use a different quote type inside the braces than the one around the string, for example an f-string delimited by double quotes with single quotes for the dict key inside. 2. Move the awkward expression out of the f-string. Compute it first (name = data["key"]; joined = "\n".join(items)) and interpolate only the simple variable. This also fixes the backslash error, since backslashes are fine outside the braces. 3. For nesting, build the inner string in a separate variable, or use str.format or concatenation. 4. If the project can require it, upgrade to Python 3.12 or newer and set python_requires (or requires-python) accordingly, so contributors and CI do not use an older interpreter by mistake. 5. Check which interpreter actually runs: python --version, and in CI/Docker confirm the image tag. A mismatch between a local 3.12 and a deployed 3.10/3.11 is the usual cause of "works on my machine". Verify: python -m py_compile yourfile.py succeeds under the oldest interpreter you support, and the test suite passes on every Python version in your CI matrix. Sources: https://peps.python.org/pep-0701/ https://docs.python.org/3/whatsnew/3.12.html