Parameter#

class astropy.cosmology.Parameter(*, default: Any = Sentinel.MISSING, derived: bool = False, unit: _UnitField = None, equivalencies: u.Equivalency | Sequence[u.Equivalency] = <factory>, fvalidate: _FValidateField = 'default', doc: str | None = None)[source]#

Bases: object

Cosmological parameter (descriptor).

Should only be used with a Cosmology subclass.

Parameters:

defaultAny (optional, keyword-only): Default value of the Parameter. If not given the Parameter must be set when initializing the cosmology.
derivedbool (optional, keyword-only): Whether the Parameter is ‘derived’, default False. Derived parameters behave similarly to normal parameters, but are not sorted by the Cosmology signature (probably not there) and are not included in all methods. For reference, see Ode0 in FlatFLRWMixin, which removes \(\Omega_{de,0}`\) as an independent parameter (\(\Omega_{de,0} \equiv 1 - \Omega_{tot}\)).
unitastropy:unit-like or None (optional, keyword-only): The Unit for the Parameter. If None (default) no unit as assumed.
equivalenciesEquivalency or sequence thereof: Unit equivalencies for this Parameter.
fvalidatecallable()[[object, object, Any], Any] or str (optional, keyword-only): Function to validate the Parameter value from instances of the cosmology class. If “default”, uses default validator to assign units (with equivalencies), if Parameter has units. For other valid string options, see Parameter._registry_validators. ‘fvalidate’ can also be set through a decorator with validator().
docstr or None (optional, keyword-only): Parameter description.

Examples

For worked examples see FLRW.

Attributes Summary

`default`	Default value of the Parameter.
`derived`	Whether the Parameter can be set, or is derived, on the cosmology.
`doc`	Parameter description.
`fvalidate`	Function to validate/convert values when setting the Parameter.
`name`	The name of the Parameter on the Cosmology.
`unit`	The unit of the Parameter (can be `None` for unitless).

Methods Summary

`clone`(**kw)	Clone this `Parameter`, changing any constructor argument.
`register_validator`(key[, fvalidate])	Decorator to register a new kind of validator function.
`validate`(cosmology, value)	Run the validator on this Parameter.
`validator`(fvalidate)	Make new Parameter with custom `fvalidate`.

Attributes Documentation

default: Any = 1#

Default value of the Parameter.

By default set to MISSING, which indicates the parameter must be set when initializing the cosmology.

derived: bool = False#: Whether the Parameter can be set, or is derived, on the cosmology.

doc: str | None = None#: Parameter description.

fvalidate: _FValidateField = 'default'#: Function to validate/convert values when setting the Parameter.

name: str | None = None#

The name of the Parameter on the Cosmology.

Cannot be set directly.

unit: _UnitField = None#: The unit of the Parameter (can be None for unitless).

Methods Documentation

clone(**kw)[source]#

Clone this Parameter, changing any constructor argument.

Parameters:

**kw: Passed to constructor. The current values, eg. fvalidate are used as the default values, so an empty **kw is an exact copy.

Examples

>>> p = Parameter()
>>> p
Parameter(derived=False, unit=None, equivalencies=[],
          fvalidate='default', doc=None)

>>> p.clone(unit="km")
Parameter(derived=False, unit=Unit("km"), equivalencies=[],
          fvalidate='default', doc=None)

static register_validator(key, fvalidate=None)[source]#

Decorator to register a new kind of validator function.

Parameters:

keystr
fvalidatecallable()[[object, object, Any], Any] or None, optional: Value validation function.

Returns:

validator or callable()[validator]: if validator is None returns a function that takes and registers a validator. This allows register_validator to be used as a decorator.

validate(cosmology, value)[source]#

Run the validator on this Parameter.

Parameters:

cosmologyCosmology instance
valueAny: The object to validate.

Returns:

Any: The output of calling fvalidate(cosmology, self, value) (yes, that parameter order).

validator(fvalidate)[source]#

Make new Parameter with custom fvalidate.

Note: Parameter.fvalidator must be the top-most descriptor decorator.

Parameters:

fvalidatecallable()[[type, type, Any], Any]

Returns:

Parameter: Copy of this Parameter but with custom fvalidate.