>>> import io
>>> d = io.open('.')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IsADirectoryError: [Errno 21] Is a directory: '.'
>>> 

>>> import os
>>> d = io.open(os.open('.',0))
>>> d
<_io.TextIOWrapper name=3 mode='r' encoding='UTF-8'>
>>>

io.open() clearly doesn't care about opening directories as long as they are passed as os.open() file descriptors. Quite unexpected!

Good catch indeed.

Note that attempting subsequent operations on the returned object do raise IsADirectoryError.


>>> import io
>>> import os
>>> d = io.open(os.open('.',0))
>>> d.read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IsADirectoryError: [Errno 21] Is a directory
>>>

New changeset 9cf9527358a5 by Antoine Pitrou in branch '3.2':
Issue #15247: FileIO now raises an error when given a file descriptor pointing to a directory.
http://hg.python.org/cpython/rev/9cf9527358a5

New changeset 19bd61ed3b3b by Antoine Pitrou in branch 'default':
Issue #15247: FileIO now raises an error when given a file descriptor pointing to a directory.
http://hg.python.org/cpython/rev/19bd61ed3b3b

New changeset d7040647d590 by Antoine Pitrou in branch '2.7':
Issue #15247: FileIO now raises an error when given a file descriptor pointing to a directory.
http://hg.python.org/cpython/rev/d7040647d590

Thanks, the issue should be fixed now.