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 execute_as(self, user):
        self.check_prereq(self.LOGGED_IN)
        self._exit_modes_beyond(self.LOGGED_IN)
        user.commandLine(self)
        user.login()
        self.modeList.append(user)
        return user