Python 'SyntaxError: invalid syntax' on a match statement, walrus operator (:=) or other new syntax that works on my machine but fails on a server or in CI. How do I fix Python version mismatches?

Cause: newer syntax only parses on newer Python versions. Structural pattern matching (match/case) needs Python 3.10+, assignment expressions (the walrus operator :=) and positional-only parameters (/) need 3.8+, parenthesized context managers are official from 3.10, and newer f-string flexibility (nested quotes) needs 3.12. When code runs on an older interpreter (system Python on an older Linux, an old Docker base image, a CI runner default, or an IDE pointing at a different interpreter), Python fails at parse time with a SyntaxError on the first new construct, before any code runs. Fix: 1. Check which Python actually runs the code: python --version, and in scripts import sys; print(sys.version) (or look at the shebang line, CI logs, and the Docker image tag). 2. Run on a version that supports the syntax: update the Docker base image (python:3.12-slim etc.), set the version in CI (actions/setup-python python-version), or install a newer Python with your OS packages, pyenv or uv, and create the venv from it. 3. Declare the minimum version so tools catch this early: requires-python = ">=3.10" in pyproject.toml makes pip refuse to install the project on older Pythons. 4. If you must support an older Python, rewrite the construct (if/elif instead of match; a separate assignment instead of :=) and run your tests on the oldest supported version in CI. 5. Use a linter or type checker configured with your target version (e.g. ruff's target-version) to flag syntax that's too new. Verify: python --version in the failing environment shows a version that supports the syntax, and the script runs; CI tests pass on every version you claim to support. Sources: https://docs.python.org/3/whatsnew/3.10.html https://docs.python.org/3/whatsnew/3.8.html