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#term-n.

-like#

<Class>-like is an instance of the Class or a valid initializer argument for Class as Class(value). E.g. Quantity-like includes "2 * u.km" because astropy.units.Quantity("2 * u.km") works.

[‘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 and a valid initializer for Angle. The unit must be an angular. A string input is interpreted as an angle as described in the Angle documentation.

buffer-like#

Object that implements Python’s buffer protocol.

coordinate-like#

BaseCoordinateFrame subclass instance, or a SkyCoord (or subclass) instance, or a valid initializer as described in COORD.

file-like (readable)#

python:file-like object object that supports reading with a method read.

For a formal definition see ReadableFileLike.

file-like (writeable)#

python:file-like object object that supports writing with a method write.

For a formal definition see WriteableFileLike.

frame-like#

BaseCoordinateFrame subclass or subclass instance or a valid Frame name (string).

length-like#

quantity-like and a valid initializer for Distance. The unit must be a convertible to a unit of length.

number#

Any scalar numeric type. e.g. float or int or numpy.number.

quantity-like#

Quantity (or subclass) instance, a number or array-like object, or a string which is a valid initializer for Quantity.

For a formal definition see QuantityLike.

table-like#

Table (or subclass) instance or valid initializer for Table as described in Constructing a Table. Common types include dict[list], list[dict], list[list], and ndarray (structured array).

time-like#

Time (or subclass) instance or a valid initializer for Time, e.g. str, array-like[str], datetime, or datetime64.

trait type#

In short, a trait type is a class with the following properties:

  • It is a class that can be used as a mixin to add functionality to another class.

  • It should never be instantiated directly.

  • It should not be used as a base class for other classes, but only as a mixin.

  • It can define methods, properties, and attributes – any of which can be abstract.

  • It can be generic, i.e. it can have type parameters.

  • It can subclass other traits, but should have a linear MRO.

These are the same set of properties as orthogonal mixin classes, with the added emphasis that they can serve as compiled types, if so enabled by a compilation system such as mypyc.

unit-like#

UnitBase subclass instance or a valid initializer for Unit, e.g., str or scalar Quantity.

Optional Packages’ Glossary#

color#

Any valid Matplotlib color.