I guessed you did it this way because it was simple and perhaps a native reader would be overoptimizing compared to constructing the graph. I think writing the reader in rust (with a Python interface) is perhaps fair. It certainly would be if the graph format were a solid standard (it is not). I was spending some time getting the parsing as fast as I could in Julia (I posted here ) But, constructing a graph with weights swamped this time. It would be easy to test your python reader at just parsing (has the advantage of being very readable code) vs. Julia at just parsing.