I don't have a big file handy to benchmark but that pattern moves the file reading into python bytecode.

The canonical way to read a file line by line while counting the lines is to loop over the file (it's automatically a line iterator) and use enumerate.

here is the disassembed bytecode of the respective versions

https://pastebin.com/Rd4g8cE2

that being said, Rust will still outrun Python overall.