file io - Python "FileExists" error when making directory

Question

I have several threads running in parallel from Python on a cluster system. Each python thread outputs to a directory mydir. Each script, before outputting checks if mydir exists and if not creates it:

if not os.path.isdir(mydir):
    os.makedirs(mydir)

but this yields the error:

os.makedirs(self.log_dir)                                             
  File "/usr/lib/python2.6/os.py", line 157, in makedirs
mkdir(name,mode)
OSError: [Errno 17] File exists

I suspect it might be due to a race condition, where one job creates the dir before the other gets to it. Is this possible? If so, how can this error be avoided?

I'm not sure it's a race condition so was wondering if other issues in Python can cause this odd error.

Answer 1

As of Python >=3.2, os.makedirs() can take a third optional argument exist_ok:

os.makedirs(mydir, exist_ok=True)