xarray development setup

Setup

Development environments are managed with pixi, the same ones CI uses (see [environments] in pixi.toml). They are installed on first use.

Run tests

pixi run -e test-py313 -- python -m pytest xarray -n auto  # All tests in parallel
pixi run -e test-py313 -- python -m pytest xarray/tests/test_dataarray.py  # Specific file

Environments like test-py314-no-dask or test-py312-bare-minimum run the tests without some optional dependencies.

See xarray/tests/AGENTS.md for guidelines on writing tests.

Linting & type checking

pixi exec pre-commit run --all-files  # Includes ruff and other checks
pixi run -e test-py314-with-typing -- python -m mypy  # Type checking with mypy

Code Style Guidelines

Import Organization

• Always place imports at the top of the file in the standard import section
• Never add imports inside functions or nested scopes unless there's a specific reason (e.g., circular import avoidance, optional dependencies in TYPE_CHECKING)
• Group imports following PEP 8 conventions:
  1. Standard library imports
  2. Related third-party imports
  3. Local application/library specific imports

Type hints

• Always add type hints to every function and method you create or edit, including tests (-> None), fixtures and helpers

CI

• The test-py314 (flaky) job runs tests that depend on external services (e.g. test.opendap.org) and fails regularly for unrelated reasons. It does not block merging, so don't skip or change these tests, ask for reruns, or explain these failures in PRs.

GitHub Interaction Guidelines

• NEVER impersonate the user on GitHub, always sign off with something like "[This is <tool name> on behalf of Jane Doe]"
• Never create issues nor pull requests on the xarray GitHub repository unless explicitly instructed
• Never post "update" messages, progress reports, or explanatory comments on GitHub issues/PRs unless specifically instructed
• Don't comment on an issue to ask to be assigned or to announce that you are working on it or will open a PR. xarray does not assign issues: just open the PR and reference the issue in its description.
• When creating commits, always include a co-authorship trailer for the tool, e.g. Co-authored-by: Claude <noreply@anthropic.com>