human
Here's a good function header given the following:
I wrote the below code

    if (values is None):
        if ((default in (True, False)) or ((type(default) is str) and (default.upper() in ('TRUE', 'FALSE')))):
            values = (True, False)
        else:
            values = (lambda x: True)
    if (default is None):
        default = (False if (values == (True, False)) else '')
    default = default
    description = str(description).strip()
    def _execute(pkg):
        if (not re.match(spack.spec.identifier_re, name)):
            directive = 'variant'
            msg = "Invalid    variant    name    in    {0}:    '{1}'"
            raise DirectiveError(directive, msg.format(pkg.name, name))
        pkg.variants[name] = Variant(name, default, description, values, multi, validator)
    return _execute

What's a good function header?
assistant
#Here's a good function header.

@directive('variants')
def variant(name, default=None, description='', values=None, multi=False, validator=None):