os.makedirs first checks if the non-leaf part of the path exists, and then calls makedirs on this part of the path to create it. If the path is created in between the call to path.exists, and the recursive call to os.makedirs, then  os.makedirs will raise an exception.

The attached patch catches this exception, and then tests if the exception is caused by a the file/directory's existence. If it is, the exception is ignored. If not, it is rasied.