Source code for pinttr.validators

from ._metadata import MetadataKey
from .exceptions import UnitsError
from .util import units_compatible




def has_compatible_units(instance, attribute, value):
    """
    Validate if ``value`` has units compatible (in the sense of
    :func:`~pinttr.units_compatible`) with ``attribute``.

    This validator checks that a Pint quantity has units compatible with the
    units declared for an attribute. It raises :class:`~pinttrs.exceptions.UnitsError`
    if the units are incompatible or if a unitless value is provided.

    Only works with unit-enabled fields created with :func:`pinttrs.field` or
    :func:`pinttr.attrib`.

    :param instance:
        The class instance being validated.

    :param attribute:
        The attrs attribute being validated (must have units metadata).

    :param value:
        The value to validate (should be a Pint quantity).

    :raises  UnitsError:
        If units are incompatible or if a unitless value is provided.
    """

    compatible_units = attribute.metadata[MetadataKey.UNITS]()

    try:
        if not units_compatible(value.units, compatible_units):
            raise UnitsError(
                units1=value.units,
                units2=compatible_units,
                extra_msg=f": incompatible units '{value.units}' "
                f"used to set field '{attribute.name}' "
                f"(allowed: '{compatible_units}').",
            )

    except AttributeError:  # value.units doesn't exist
        raise UnitsError(
            units1=None,
            units2=compatible_units,
            extra_msg=f": unitless value '{value}' "
            f"used to set field '{attribute.name}' "
            f"(requires units '{compatible_units}').",
        )