I isolate the bug. It happens in these lines:

        # Always try reading and writing directly on the tty first.
        fd = os.open('/dev/tty', os.O_RDWR|os.O_NOCTTY)
        tty = os.fdopen(fd, 'w+', 1)

So to produce the bug more specifically, you can try this python file:

# bugme2.py
import os

fd = os.open('/dev/tty', os.O_RDWR|os.O_NOCTTY)
os.fdopen(fd, 'w+', 1)
# end of bugme2.py

In Linux Fedora 18, I would get this error:

/home/sky/Code/python/programming_language/cpython/Lib/os.py:1025: ResourceWarning: unclosed file <_io.FileIO name=3 mode='rb+'>
  return io.open(fd, *args, **kwargs)
Traceback (most recent call last):
  File "/tmp/bugme2.py", line 4, in <module>
    os.fdopen(fd, 'w+', 1)
  File "/home/sky/Code/python/programming_language/cpython/Lib/os.py", line 1025, in fdopen
    return io.open(fd, *args, **kwargs)
io.UnsupportedOperation: File or stream is not seekable.