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.. 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. :class:`~astropy.units.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 `~astropy.units.Quantity` (or similar :term:`quantity-like`).
For example, ``distance : quantity-like ['length']``
angle-like
:term:`quantity-like` and a valid initializer for `~astropy.coordinates.Angle`.
The ``unit`` must be an angular. A string input is interpreted as an angle as
described in the `~astropy.coordinates.Angle` documentation.
buffer-like
Object that implements `Python's buffer protocol
<https://docs.python.org/3/c-api/buffer.html#bufferobjects>`_.
coordinate-like
:class:`~astropy.coordinates.BaseCoordinateFrame` subclass instance, or a
:class:`~astropy.coordinates.SkyCoord` (or subclass) instance, or a valid
initializer as described in :ref:`coordinates-initialization-coord`.
file-like (readable)
:term:`python:file-like object` object that supports reading with a method ``read``.
For a formal definition see :class:`~astropy.io.typing.ReadableFileLike`.
file-like (writeable)
:term:`python:file-like object` object that supports writing with a method ``write``.
For a formal definition see :class:`~astropy.io.typing.WriteableFileLike`.
frame-like
:class:`~astropy.coordinates.BaseCoordinateFrame` subclass or subclass instance or
a valid Frame name (string).
length-like
:term:`quantity-like` and a valid initializer for
:class:`~astropy.coordinates.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
`~astropy.units.Quantity` (or subclass) instance, a number or `array-like
<https://numpy.org/doc/stable/glossary.html#term-array_like>`_ object, or a string
which is a valid initializer for `~astropy.units.Quantity`.
For a formal definition see :obj:`~astropy.units.typing.QuantityLike`.
table-like
:class:`~astropy.table.Table` (or subclass) instance or valid initializer for
:class:`~astropy.table.Table` as described in :ref:`construct_table`. Common types
include ``dict[list]``, ``list[dict]``, ``list[list]``, and `~numpy.ndarray`
(structured array).
time-like
:class:`~astropy.time.Time` (or subclass) instance or a valid initializer for
:class:`~astropy.time.Time`, e.g. `str`, array-like[str], `~datetime.datetime`, or
`~numpy.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 <https://mypyc.readthedocs.io/en/latest/>`_.
unit-like
:class:`~astropy.units.UnitBase` subclass instance or a valid initializer for
:class:`~astropy.units.Unit`, e.g., `str` or scalar `~astropy.units.Quantity`.