Cannot launch Ipython3. OSError: [Errno 9] Bad file descriptor

Python 3.5.2+ (default, Sep 22 2016, 12:18:14) 
Type 'copyright', 'credits' or 'license' for more information
IPython 6.0.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]:                                                                                                                                               
Traceback (most recent call last):
  File "/usr/local/bin/ipython3", line 11, in <module>
    sys.exit(start_ipython())
  File "/usr/local/lib/python3.5/dist-packages/IPython/__init__.py", line 125, in start_ipython
    return launch_new_instance(argv=argv, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/traitlets/config/application.py", line 658, in launch_instance
    app.start()
  File "/usr/local/lib/python3.5/dist-packages/IPython/terminal/ipapp.py", line 353, in start
    self.shell.mainloop()
  File "/usr/local/lib/python3.5/dist-packages/IPython/terminal/interactiveshell.py", line 459, in mainloop
    self.interact()
  File "/usr/local/lib/python3.5/dist-packages/IPython/terminal/interactiveshell.py", line 442, in interact
    code = self.prompt_for_code()
  File "/usr/local/lib/python3.5/dist-packages/IPython/terminal/interactiveshell.py", line 355, in prompt_for_code
    pre_run=self.pre_prompt, reset_current_buffer=True)
  File "/usr/local/lib/python3.5/dist-packages/prompt_toolkit/interface.py", line 411, in run
    with self.input.raw_mode():
  File "/usr/local/lib/python3.5/dist-packages/prompt_toolkit/terminal/vt100_input.py", line 473, in __enter__
    os.write(self.fileno, b'\x1b[?1l')
OSError: [Errno 9] Bad file descriptor

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[malthejorgensen]

This happened to me on OS X 10.12.6 in a long lived tmux tab. I use fish as my shell. Starting the iPython REPL in any of the other tabs in the same tmux session worked. Reconnecting to the session and trying in the same tab still gave the same error.

In my case I believe, something happened to that particular fish session.

[refi64]

I actually think this is an IPython bug. Here’s what I’ve found:

In many cases, stdout and stdin both are pointing to the same PTY device, so if they’re open as read-write, writing to stdin is actually writing to stdout, and reading from stdout is actually reading from stdin. You can observe this by running: os.write(0, b'test\n') in Python: it’ll write to the same PTY.

However, according to the posix standard, nothing is mentioned about stdin being writable or stdout being readable. (It does say that stderr must be rw.)

Thus, in this case, I think IPython could get identical behavior by writing to stdout instead. In theory this would differ if stdin were a tty and stdout were a different one, but tbh I’ve never seen that before, and I’m not sure what exactly would be going on there or what type of behavior would even be expected.

Please feel free to correct anything here that seems off, but I thought this would at least be something worth adding to the discussion.