Optional convert

[cossatot]

Is it, or could it be, possible to have optional type conversion using the convert argument, with the same logic as validation?

Something like:

@attr.s
class Thing(object):
    x = attr.ib(default=None, convert=optional(float), validator=optional(validate_x))

Apologies if it's already supported; I just don't see how in the docs.

[Tinche]

You can write this yourself, easily (and I have in one of my projects):

def opt(convert):
    """Invoke the subconverter only if the value is present."""
    def optional_converter(val):
        if val is None:
            return None
        return convert(val)
    return optional_converter

Now, I don't think it'd be possible to use the same callable (optional) as a validator factory AND a convert factory without changes to attrs itself.

[cossatot]

Thanks, that's exactly what i was looking for.

[hynek]

I guess it would make sense to add it to attrs?