内核死亡，自动重启失败

Question

I am getting the following error when I run ipython notebook from directory with contains a file named cmd.py

So my question is WHY? because everything is perfect when I rename or remove the file.

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/me/.virtualenvs/demo/lib/python3.4/site-packages/IPython    /__init__.py", line 48, in <module>
    from .core.application import Application
  File "/home/me/.virtualenvs/demo/lib/python3.4/site-packages/IPython    /core/application.py", line 40, in <module>
    from IPython.core import release, crashhandler
  File "/home/me/.virtualenvs/demo/lib/python3.4/site-packages/IPython    /core/crashhandler.py", line 28, in <module>
    from IPython.core import ultratb
  File "/home/me/.virtualenvs/demo/lib/python3.4/site-packages/IPython/core/ultratb.py", line 110, in <module>
    from IPython.core import debugger
  File "/home/me/.virtualenvs/demo/lib/python3.4/site-packages/IPython/core/debugger.py", line 59, in <module>
    from pdb import Pdb as OldPdb
  File "/usr/local/lib/python3.4/pdb.py", line 135, in <module>
    class Pdb(bdb.Bdb, cmd.Cmd):
AttributeError: 'module' object has no attribute 'Cmd'
2015-01-14 22:23:36.895 [NotebookApp] WARNING | KernelRestarter: restart failed
2015-01-14 22:23:36.896 [NotebookApp] WARNING | Kernel 1005e1cf-b1b4-4f9d-        af22-e65c310cfa51 died, removing from map.
ERROR:root:kernel 1005e1cf-b1b4-4f9d-af22-e65c310cfa51 restarted failed!

Answer 1

The last lines of your traceback show that CPython's module pdb is being imported while IPython starts up. Line 72 of the pdb.py source shows that another module called cmd is imported by "pdb.py".

The Python docs show the following order when searching for imports, which I believe is the same for IPython:

1. Current working directory
2. PYTHONPATH
3. Installation dependent defaults

Since the startup process involves an import of a module called cmd and there is a file called "cmd.py" in the first place the interpreter looks, it attempts to import that file, which of course doesn't have the things it's looking for. Specifically, your file "cmd.py" doesn't have the Cmd class , so the AttributeError is raised.

Removing or renaming "cmd.py" in your current working directory will resolve the issue.

Answer 2

Open a Python interpreter session, and run the following:

import sys
from pprint import pprint as pp

pp(sys.path)

You'll notice that the first entry is '' , which means the current directory. When pdb tries to import a module named cmd , it's actually importing the file in your current directory, which (I would assume) doesn't have the code it's looking for. Removing or renaming that file fixes your problem.

Answer 3

I just ran across this problem and started to frantically search for a reason why the kernel is dying. For myself, at least, the solution came to me by trial and error.

I tried opening a new notebook in another directory and the kernel did not die there. So I figured out that the kernel was dying only for that specific directory path. The reason behind this was: I already had an active session of iPython with that very directory path on another machine. As soon as I ended the session on the other machine, problem solved.