SyntaxError: invalid syntax

Python SyntaxError most often signals a Python 2 vs Python 3 compatibility issue or a feature requiring a newer Python 3 version. The print statement (print 'hello') is valid in Python 2 but a SyntaxError in Python 3.0+. If you are running Python 3 and see SyntaxError on a print line, you are reading Python 2 code. Version-specific syntax features have strict minimum versions: f-strings require Python 3.6+; the walrus operator (:=) requires Python 3.8+; positional-only parameters (def f(a, /, b)) require Python 3.8+; structural pattern matching (match/case) requires Python 3.10+; ExceptionGroup syntax requires Python 3.11+. Using these features in Docker containers or CI environments running older Python versions produces SyntaxError even when your local machine runs Python 3.12. Ubuntu 18.04 LTS ships Python 3.6 as the system default. Ubuntu 20.04 ships Python 3.8. If your CI runner uses an Ubuntu 18.04 base image — common in older self-hosted GitHub Actions setups — Python 3.8+ walrus operator syntax causes SyntaxError. Always pin the Python version in CI using actions/setup-python with the same version as in your .python-version or pyproject.toml requires-python field.