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 _format_traceback(cls, traceback_lines, should_print_backtrace):
        if should_print_backtrace:
            traceback_string = "\n{}".format("".join(traceback_lines))
        else:
            traceback_string = " {}".format(cls._traceback_omitted_default_text)
        return traceback_string