Custom registry class#

Pay as you go#

Pint registry functionality is divided into facets. The default UnitRegistry inherits from all of them, providing a full fledged and feature rich registry. However, in certain cases you might want to have a simpler and light registry. Just pick what you need and create your own.

  • FormattingRegistry: adds the capability to format quantities and units into string.

  • SystemRegistry: adds the capability to work with system of units.

  • GroupRegistry: adds the capability to group units.

  • MeasurementRegistry: adds the capability to handle measurements (quantities with uncertainties).

  • NumpyRegistry: adds the capability to interoperate with NumPy.

  • DaskRegistry: adds the capability to interoperate with Dask.

  • ContextRegistry: the capability to contexts: predefined conversions between incompatible dimensions.

  • NonMultiplicativeRegistry: adds the capability to handle nonmultiplicative units (offset, logarithmic).

  • PlainRegistry: base implementation for registry, units and quantities.

The only required one is PlainRegistry, the rest are completely optional.

For example:

>>> import pint
>>> class MyRegistry(pint.facets.NonMultiplicativeRegistry, pint.facets.PlainRegistry):
...     pass

Subclassing#

If you want to add the default registry class some specific functionality, you can subclass it:

>>> import pint
>>> class MyRegistry(pint.UnitRegistry):
...
...     def my_specific_function(self):
...         """Do something
...         """

If you want to create your own Quantity class, you must tell your registry about it:

>>> import pint
>>> class MyQuantity:
...
...     # Notice that subclassing pint.Quantity
...     # is not necessary.
...     # Pint will inspect the Registry class and create
...     # a Quantity class that contains all the
...     # required parents.
...
...     def to_my_desired_format(self):
...         """Do something else
...         """
>>>
>>> class MyRegistry(pint.UnitRegistry):
...
...     _quantity_class = MyQuantity
...
...     # The same you can be done with
...     # _unit_class
...     # _measurement_class

While these examples demonstrate how to add functionality to the default registry class, you can actually subclass just the PlainRegistry or any combination of facets.