astropy.units.def_physical_type(unit, name)[source]

Add a mapping between a unit and the corresponding physical type(s).

If a physical type already exists for a unit, add new physical type names so long as those names are not already in use for other physical types.


The unit to be represented by the physical type.

namestr or set of str

A str representing the name of the physical type of the unit, or a set containing strings that represent one or more names of physical types.


If a physical type name is already in use for another unit, or if attempting to name a unit as "unknown".