setters

def convert(instance, attrib, new_value):
    """
    Run *attrib*'s converter -- if it has one --  on *new_value* and return the
    result.

    .. versionadded:: 20.1.0
    """
    c = attrib.converter
    if c:
        return c(new_value)

    return new_value

def frozen(_, __, ___):
    """
    Prevent an attribute to be modified.

    .. versionadded:: 20.1.0
    """
    raise FrozenAttributeError()

def pipe(*setters):
    """
    Run all *setters* and return the return value of the last one.

    .. versionadded:: 20.1.0
    """

    def wrapped_pipe(instance, attrib, new_value):
        rv = new_value

        for setter in setters:
            rv = setter(instance, attrib, rv)

        return rv

    return wrapped_pipe

def validate(instance, attrib, new_value):
    """
    Run *attrib*'s validator on *new_value* if it has one.

    .. versionadded:: 20.1.0
    """
    if _config._run_validators is False:
        return new_value

    v = attrib.validator
    if not v:
        return new_value

    v(instance, attrib, new_value)

    return new_value