def remove(self, elem):
        """Remove a requirement.

        :param elem: a string or :class:`Requirement` instance.
        """
        if isinstance(elem, text_type):
            for requirement in self:
                if requirement.package == elem:
                    return super(Requirements, self).remove(requirement)
        return super(Requirements, self).remove(elem)
def call_process(cls, cmd):
        if cls.is_error:
            raise subprocess.CalledProcessError(-1, cmd=cmd, output="Couldn't call xset.")

        if cmd[1:] == ["q"]:
            track = cls.info[cls.index]
            output = "\n".join(track)
            return output