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

    @event.listens_for(col_attr, 'init_scalar', retval=True, propagate=True)
    def init_scalar(target, value, dict_):
        if default.is_callable:
            value = default.arg(None)
        elif default.is_scalar:
            value = default.arg
        else:
            raise NotImplementedError("Can't    invoke    pre-default    for    a    SQL-level    column    default")
        dict_[col_attr.key] = value
        return value

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

def default_listener(col_attr, default):