def __repr__(self):
        return "<Requirement(package={package}, version='{version}')>".format(
            package=self.package, version=self.version)
def get_leafs(self):
		if self.lchild == None and self.rchild == None:
			return [self.leaf]
		else:
			return self.lchild.get_leafs()+self.rchild.get_leafs()