Oh, I'm sorry, I forgot about that case. 

I agree with Arfrever, we should suppress the OSError only if the target file exists as a directory, but not other types. That is, the "exist_ok" argument in makedirs() should mean "dir existing is ok", only existing of the exact same thing as we specified to create is ok, not other things. I will fixed this later. 

Besides, I wonder what should we do if the target directory exists but with a different mode than we specified(if we specified the "mode" argument). I guess we should also raise the OSError because the existing thing is not the same as what we want.