code: def read_pid(self):
          
          try:
              with open(self._path, 'r') as f:
                  s = f.read().strip()
                  if not s:
                      return None
                  return int(s)
          except IOError as e:
              if e.errno == errno.ENOENT:
                  return None
              raise
docs: Return the PID of the process owning the lock.
  
          Returns ``None`` if no lock is present.