>>> from shutil import make_archive; make_archive("a", "tar")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.4/shutil.py", line 783, in make_archive
    filename = func(base_name, base_dir, **kwargs)
  File "/usr/lib/python3.4/shutil.py", line 605, in _make_tarball
    os.makedirs(archive_dir)
  File "/usr/lib/python3.4/os.py", line 244, in makedirs
    mkdir(name, mode)
FileNotFoundError: [Errno 2] No such file or directory: ''

Looking at the code, it calls os.path.dirname("a.tar") -> "", which would be the cause of this bug.

The workaround for me was adding an explicit make_archive(root_dir=".") parameter.

I was also surprised to see the code calling os.makedirs(archive_dir). Usually if you try to make a file in a non-existent directory, it fails, rather than automatically creating the directory for you. But maybe that’s just a general spirit of the “shutil” module that I didn’t pick up on.