Python: Lock a directory

Question

I have a python script which gets executed via cron every 5 minutes.

This script operates on a directory.

Sometimes it takes longer then 5 minutes and I want to avoid that two jobs run in parallel.

I tried to use the library flockcontext but this can only lock files.

I get this exception:

   with flockcontext.FlockOpen(directory, 'r'):
  File "/.../flockcontext/flock_open.py", line 54, in __enter__
    self.fd = open(self._filepath, self._mode)
IOError: [Errno 21] Is a directory: 'my-dir'

How to lock a directory with a context manager?

I know that I could work-around this issue by locking a file (maybe var/lock/foo), but I would like to have a solution (not a work-around).

PS: I know that this lock only prevents other processes to operate on this directory who check this lock before starting.