title: Check if line is a timestamp in Python
body: <p>I have a script that runs every 30 minutes on my server, and when it's done it writes a timestamp to the last line of the file. It does this to about 20+ files in one directory. I'm trying to write a Python script to check the last line of each file and return either a "In progress" or "Finished at:" message for each file depending on if that timestamp is present or not. </p>
  
  <p>How do I get Python to determine if a string is a timestamp or not? It is formatted as HH:MM:SS, no month/date indications. </p>