FunctionQuantity

class astropy.units.function.FunctionQuantity

Bases: astropy.units.quantity.Quantity

A representation of a (scaled) function of a number with a unit.

Function quantities are quantities whose units are functions containing a physical unit, such as dB(mW). Most of the arithmetic operations on function quantities are defined in this base class.

While instantiation is also defined here, this class should not be instantiated directly. Rather, subclasses should be made which have _unit_class pointing back to the corresponding function unit class.

Parameters:

value : number, sequence of convertible items, Quantity, or FunctionQuantity

The numerical value of the function quantity. If a number or a Quantity with a function unit, it will be converted to unit and the physical unit will be inferred from unit. If a Quantity with just a physical unit, it will converted to the function unit, after, if necessary, converting it to the physical unit inferred from unit.

unit : string, UnitBase or FunctionUnitBase instance, optional

For an FunctionUnitBase instance, the physical unit will be taken from it; for other input, it will be inferred from value. By default, unit is set by the subclass.

dtype : dtype, optional

The dtype of the resulting Numpy array or scalar that will hold the value. If not provided, it is determined from the input, except that any input that cannot represent float (integer and bool) is converted to float.

copy : bool, optional

If True (default), then the value is copied. Otherwise, a copy will only be made if __array__ returns a copy, if value is a nested sequence, or if a copy is needed to satisfy an explicitly given dtype. (The False option is intended mostly for internal use, to speed up initialization where a copy is known to have been made. Use with care.)

order : {‘C’, ‘F’, ‘A’}, optional

Specify the order of the array. As in array. Ignored if the input does not need to be converted and copy=False.

subok : bool, optional

If False (default), the returned array will be forced to be of the class used. Otherwise, subclasses will be passed through.

ndmin : int, optional

Specifies the minimum number of dimensions that the resulting array should have. Ones will be pre-pended to the shape as needed to meet this requirement. This parameter is ignored if the input is a Quantity and copy=False.

Raises:

TypeError

If the value provided is not a Python numeric type.

TypeError

If the unit provided is not a FunctionUnitBase or Unit object, or a parseable string unit.

Attributes Summary

cgs	Return a copy with the physical unit in CGS units.
equivalencies	Equivalencies applied by default during unit conversions.
physical	The physical quantity corresponding the function one.
si	Return a copy with the physical unit in SI units.
unit	Function unit of the quantity, containing the physical unit.

Methods Summary

decompose([bases])	Generate a new FunctionQuantity with the physical unit decomposed.
to(unit[, equivalencies])	Returns a new quantity with the specified units.

Attributes Documentation

cgs

Return a copy with the physical unit in CGS units.

equivalencies

Equivalencies applied by default during unit conversions.

Contains the list to convert between function and physical unit, as set by the FunctionUnitBase unit.

physical

The physical quantity corresponding the function one.

si

Return a copy with the physical unit in SI units.

unit

Function unit of the quantity, containing the physical unit.

Represented by a FunctionUnitBase object.

Methods Documentation

decompose(bases=[])

Generate a new FunctionQuantity with the physical unit decomposed.

For details, see decompose.

to(unit, equivalencies=[])

Returns a new quantity with the specified units.

Parameters:

unit : UnitBase instance, str

An object that represents the unit to convert to. Must be an UnitBase object or a string parseable by the units package.

equivalencies : list of equivalence pairs, optional

A list of equivalence pairs to try if the units are not directly convertible. See Equivalencies. This list is in meant to treat only equivalencies between different physical units; the build-in equivalency between the function unit and the physical one is automatically taken into account.