Failed to start kernel on jupyter notebook

Question

I recently uninstalled Anaconda3 and reinstalled Anaconda on Python 2. Following this, it seems that I cannot get a kernel running when I work with jupyter notebooks. I get this kernel error on any notebook that I tried to open:

Failed to start kernel

Traceback (most recent call last):
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\notebook\base\handlers.py", line 516, in wrapper
    result = yield gen.maybe_future(method(self, *args, **kwargs))
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\gen.py", line 1055, in run
    value = future.result()
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\concurrent.py", line 238, in result
    raise_exc_info(self._exc_info)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\gen.py", line 1063, in run
    yielded = self.gen.throw(*exc_info)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\notebook\services\sessions\handlers.py", line 75, in post
    type=mtype))
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\gen.py", line 1055, in run
    value = future.result()
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\concurrent.py", line 238, in result
    raise_exc_info(self._exc_info)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\gen.py", line 1063, in run
    yielded = self.gen.throw(*exc_info)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\notebook\services\sessions\sessionmanager.py", line 79, in create_session
    kernel_id = yield self.start_kernel_for_session(session_id, path, name, type, kernel_name)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\gen.py", line 1055, in run
    value = future.result()
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\concurrent.py", line 238, in result
    raise_exc_info(self._exc_info)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\gen.py", line 1063, in run
    yielded = self.gen.throw(*exc_info)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\notebook\services\sessions\sessionmanager.py", line 92, in start_kernel_for_session
    self.kernel_manager.start_kernel(path=kernel_path, kernel_name=kernel_name)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\gen.py", line 1055, in run
    value = future.result()
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\concurrent.py", line 238, in result
    raise_exc_info(self._exc_info)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\tornado\gen.py", line 307, in wrapper
    yielded = next(result)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\notebook\services\kernels\kernelmanager.py", line 94, in start_kernel
    super(MappingKernelManager, self).start_kernel(**kwargs)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\jupyter_client\multikernelmanager.py", line 110, in start_kernel
    km.start_kernel(**kwargs)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\jupyter_client\manager.py", line 257, in start_kernel
    **kw)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\jupyter_client\manager.py", line 203, in _launch_kernel
    return launch_kernel(kernel_cmd, **kw)
  File "C:\Users\Ejer\Anaconda2\lib\site-packages\jupyter_client\launcher.py", line 128, in launch_kernel
    proc = Popen(cmd, **kwargs)
  File "C:\Users\Ejer\Anaconda2\lib\subprocess.py", line 390, in __init__
    errread, errwrite)
  File "C:\Users\Ejer\Anaconda2\lib\subprocess.py", line 640, in _execute_child
    startupinfo)
WindowsError: [Error 2] The system cannot find the file specified

Answer 1

you mean you uninstalled python 3 and installed python2? Assuming this is what you did right click on anacona prompt and run as administrator try running this after running command prompt in admin mode

python2 -m pip install ipykernel

or

python2 -m ipykernel install --user

Answer 2

This might be because juypter is unable to find python.

Try looking in share/jupyter/kernels//kernel.json in your anaconda installation, you will see something like this.

{
 "argv": [
  "C:\\Anaconda3\\python.exe",
  "-m",
  "ipykernel_launcher",
  "-f",
  "{connection_file}"
 ],
 "display_name": "Python 3",
 "language": "python"
}

make sure that the python path under argv is correct.