I've been searching through this website and have seen multiple references to time deltas, but haven't quite found what I'm looking for. Basically, I have a list of messages that are received by a comms server and I want to calcuate the latency time between each message out and in. It looks like this: 161336.934072 - TMsg out: [O] enter order. RefID [123] OrdID [4568] 161336.934159 - TMsg in: [A] accepted. ordID [456] RefNumber [123] Mixed in with these messages are other messages as well, however, I only want to capture the difference between the Out messages and in messages with the same RefID. So far, to sort out from the main log which messages are Tmessages I've been doing this, but it's really inefficient. I don't need to be making new files everytime.: big_file = open('C:/Users/kdalton/Documents/Minicomm.txt', 'r') small_file1 = open('small_file1.txt', 'w') for line in big_file: if 'T' in line: small_file1.write(line) big_file.close() small_file1.close() How do I calculate the time deltas between the two messages and sort out these messages from the main log?