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name: tables-io description: "Use Astropy Table, QTable, unified I/O, FITS, ASCII/ECSV, VOTable, optional file-format integrations, and table/FITS command-line tools." metadata: disco-role: operating disable-model-invocation: true license: BSD 3-Clause

Tables and I/O Router

Use this sub-skill when a task centers on Astropy tables, file formats, FITS HDU operations, unified read/write behavior, or table/FITS command-line tools.

Load This When

• The user asks for Table, QTable, columns, units in tables, masked data, metadata, grouping, indexing, joining, stacking, or sorting.
• The task reads/writes FITS, ASCII, ECSV, VOTable, HDF5, Parquet, YAML, or pandas/dataframe-like objects through Astropy.
• The task uses Table.read, Table.write, fits.open, fits.info, PrimaryHDU, BinTableHDU, HDUList, Header, or FITS verification.
• The command names fitsinfo, fitsheader, fitscheck, fitsdiff, showtable-astropy, or volint are involved.

Route Away When

• FITS WCS interpretation or pixel/world conversion is central; use ../wcs-nddata/SKILL.md.
• Image display, normalization, RGB output, or fits2bitmap dominates; use ../visualization-convolution/SKILL.md.
• Unit conversion is the main difficulty; use ../units-constants/SKILL.md.
• General install/config/remote-data behavior is the main issue; use ../cli-config-data/SKILL.md.

First Actions

1. Identify the object boundary: in-memory table, FITS HDU/file, text table, VOTable, or optional backend format.
2. Prefer QTable when columns should retain Quantity and mixin objects.
3. Use explicit format= for non-obvious reads/writes; do not rely on file extension guessing when correctness matters.
4. For round-tripping units/metadata, prefer ECSV for tables unless the user requires another format.
5. For FITS, decide HDU type, extension name/index, memmap mode, verification policy, and whether the operation may mutate a file.
6. Use optional dependencies only when the selected format needs them.
7. Validate with a temporary read/write round-trip or CLI help/tiny-fixture check.

References

• references/api-reference.md lists table, FITS, registry, and selected I/O APIs.
• references/workflows.md gives table creation, ECSV/FITS round-trips, FITS HDU operations, joins, grouping, and optional format patterns.
• references/formats-and-cli.md summarizes format choices and command-line safety.
• references/troubleshooting.md covers unit loss, FITS verification warnings, memmap/lazy loading, optional dependencies, and CLI mutation hazards.

Safety and Validation

• Never run a file-mutating FITS CLI option on user data without explicit approval and a backup/copy.
• Prefer temporary output paths for format experiments.
• Check table column units and metadata after round-trip if the task depends on them.
• Use explicit HDU selection when a FITS file contains multiple extensions.

Native-Backed Validation Ideas

• Write a QTable with quantity columns to ECSV and assert units round-trip.
• Create a tiny FITS image, open it with fits.open, and assert HDU shape.
• Run fitsinfo --help, fitsheader --help, and showtable-astropy --help as parser checks.