Parametric Quantities

Constructing a ParametricQuantity and its runtime dimension checking. For the lightweight, non-parametric default, see the unxt Quantity guide.

>>> import unxt as u
>>> import unxts.parametric as up

Construction and runtime dimension checking

When a ParametricQuantity is constructed it is parametrized by the unit’s dimension. This can be specified explicitly:

>>> up.PQ["length"](1, "m")
ParametricQuantity(Array(1, dtype=int32...), unit='m')

or inferred from the unit:

>>> up.PQ(1, "m")
ParametricQuantity(Array(1, dtype=int32...), unit='m')

When given explicitly, ParametricQuantity checks the input dimensions. Here a length-parametrized class (correctly) refuses a unit of time:

>>> try:
...     up.PQ["length"](1, "s")
... except Exception as e:
...     print(e)
Physical type mismatch.

That should catch some bugs! By contrast, the default Quantity accepts the subscript as a no-op and does not check:

>>> u.Q["length"](1, "s")  # no error; subscript is informational only
Quantity(Array(1, dtype=int32...), unit='s')

Dispatch on specific dimensions

Filling a ParametricQuantity’s parameter and constructing an instance may be separated — the parametrized class is a real type, usable in plum dispatch annotations:

>>> LengthQuantity = up.PQ["length"]
>>> LengthQuantity
<class 'unxt...ParametricQuantity[PhysicalType('length')]'>

The base class AbstractParametricQuantity and the concrete unxt.Quantity are not parametric — Quantity[<dimension>] does nothing and is informational only. Explore plum for more on parametric classes.