def write_kwargs_to_attrs(cls, attrs, **kwargs):
        """Writes the given keywords to the given ``attrs``.

        If any keyword argument points to a dict, the keyword will point to a
        list of the dict's keys. Each key is then written to the attrs with its
        corresponding value.

        Parameters
        ----------
        attrs : an HDF attrs
            The ``attrs`` of an hdf file or a group in an hdf file.
        \**kwargs :
            The keywords to write.
        """
        for arg, val in kwargs.items():
            if val is None:
                val = str(None)
            if isinstance(val, dict):
                attrs[arg] = val.keys()
                # just call self again with the dict as kwargs
                cls.write_kwargs_to_attrs(attrs, **val)
            else:
                attrs[arg] = val
Writes the given keywords to the given ``attrs``.

        If any keyword argument points to a dict, the keyword will point to a
        list of the dict's keys. Each key is then written to the attrs with its
        corresponding value.

        Parameters
        ----------
        attrs : an HDF attrs
            The ``attrs`` of an hdf file or a group in an hdf file.
        \**kwargs :
            The keywords to write.