This is somewhat of a nitpick. os.rename's documentation says "If dst is a directory, OSError will be raised". On Unix, this isn't completely true. If the source is a directory and the destination is an empty directory, it'll overwrite the former with the latter. (Actually if the source is a directory the inverse is true; if dst is a file, OSError will be raised.)

In [1]: import os

In [2]: os.mkdir("aaa")

In [3]: open("aaa/blah", "w").close()

In [4]: os.mkdir("bbb")

In [5]: os.rename("aaa", "bbb")

In [6]: os.listdir("bbb")
Out[6]: ['blah']