title: Parallel Processing while writing to file
body: <p>I have a csv file with around 5million lines, I want to read every line, scrape some data then append it to the end of the line. As this takes time, I want to do this process in parallel (the computation isn't intensive on it's own so I'm not looking at multi-threading, just running in parallel).</p>
  <p>Then I want to write all the lines into a new file.</p>
  <p>I'm not sure what's the best way to do this, so far I have the loop, function but i need to write the write_to_file function and the parallelisation function. Any tips on the best way to do this and which libraries to use?</p>
  <p>Thanks!</p>