R. David Murray added the comment:
We don't generally document all exceptions that a method can raise, only those
that are relevant to its specific API. In this case, documenting the exception
answers the question, "what happens if the directory already exists?" This
question is relevant to
New submission from Enrico Bianchi:
Currently, documentation for os.mkdir() (see
https://docs.python.org/3.6/library/os.html#os.mkdir ) reports only
FileExistsError exception if directory exists. Please, add other exceptions
(e.g. FileNotFoundError if directory is created in a non existent pat
