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 get_level(self, level, queue):
		if queue == None:
			queue = []
		if level == 1:
			queue.push(self)
		else:
			if self.lchild != None:
				self.lchild.get_level(level-1, queue)
			if self.rchild != None:
				self.rchild.get_level(level-1, queue)
		return queue