What changed

For complex values, 0 padding and = alignment are both invalid. When a format spec contains both, CPython raises the zero-padding error first. RustPython returned the alignment error in the regular formatting path, and the locale-aware n path applied the checks separately.

The validation now lives in one helper used by both paths. Specs such as =08.1f and =08n report the zero-padding error; =8.1f and =8n still report the alignment error.

The regression tests cover both paths.

Tests

• cargo test -p rustpython-common format_complex_
• cargo run --release -- -m test test_complex
• cargo clippy -p rustpython-common --all-targets -- -D warnings
• cargo fmt --all -- --check

AI assistance

Codex (GPT-5) assisted with comparing CPython and RustPython behavior, drafting the implementation and regression tests, and writing this PR description.

Summary by CodeRabbit

• Bug Fixes
  • Improved validation for complex number formatting options.
  • Consistently rejects unsupported combinations of zero-padding and after-sign alignment in standard and locale-aware formatting.