code: def ssh_key(key):
          
          value = str(key)
          # Ensure the file exists locally
          if not os.path.isfile(value):
              raise Exception("File Does not Exist: %s" % key)
          return value
docs: SSH key parser validator (ensure file exists)
  
          :param key: Filename/Key to validate (ensure exists)
          :return: The filename/key passed in (if valid)
          :raises Exception if filename/key is not a valid file