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- Astropy Glossary

# Astropy Glossary

(`n`,)

  A parenthesized number followed by a comma denotes a tuple with one element. The trailing comma distinguishes a one-element tuple from a parenthesized `n`. This is from NumPy; see https://numpy.org/doc/stable/glossary.html.

number

  Any numeric type. eg float or int or any of the `numpy.number`.

-like

  Used to indicate on object of that type or that can instantiate the type. E.g. `Quantity`-like includes `"2 * u.km"` because `astropy.units.Quantity("2 * u.km")` works.

unit-like

  Must be an `UnitBase` (subclass) instance or a string or other instance parseable by `Unit`.

quantity-like

  Must be an `Quantity` (or subclass) instance or a string parseable by `Quantity`. Note that the interpretation of units in strings depends on the class – `Quantity("180d")` is 180 days, while `Angle("180d")` is 180 degrees – so check the string parses as intended for `Quantity`.

[‘physical type’]

  The physical type of a quantity can be annotated in square brackets following a `Quantity` (or similar quantity-like).

  For example, `distance : quantity-like ['length']`

angle-like

  quantity-like, but interpreted by an angular `SpecificTypeQuantity`, like `Angle` or `Longitude` or `Latitude`. Note that the interpretation of units in strings depends on the class – `Quantity("180d")` is 180 days, while `Angle("180d")` is 180 degrees – so make sure the string parses as intended for `Angle`.

length-like

  quantity-like, but interpretable by `Distance`.

frame-like

  A `BaseCoordinateFrame` subclass instance or a string that can be converted to a Frame by `_get_frame_class`.

coordinate-like

  A Coordinate-type object such as a `BaseCoordinateFrame` subclass instance or a `SkyCoord` (or subclass) instance.

table-like

  An astropy `Table` or any object that can initialize one. Anything marked as table-like will be processed through a `Table`.

time-like

  `Time` or any valid initializer.

buffer-like

  Anything that implements Python’s buffer protocol. See https://docs.python.org/3/c-api/buffer.html#bufferobjects

writable file-like object

  In the context of a python:file-like object object, anything that supports writing with a method `write`.

readable file-like object

  In the context of a python:file-like object object, anything that supports writing with a method `read`.

# Optional Packages’ Glossary

color

  Any valid Matplotlib color.