IPython Notebook - early exit from cell

I'd like to programmatically exit a cell early in IPython Notebook. exit(0), however, kills the kernel.

Whats the proper way to do this? I'd prefer not to split the cell or manually halt execution.

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小开

This is far from "proper" but one way to exit early is to create a runtime error. So instead of returning early from a script cleanly with exit(0) one can return uncleanly with something like

print(variable_to_query)
() + 1

which will run the code up until this point (completing the print statement) and then fail.

小开

Slightly more "proper" options:

This will get you out of all but the worst try/except blocks. 

raise KeyboardInterrupt

A little cleaner version of yours:

assert(False)

or simply:

raise

if you want to save a couple keystrokes.

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最佳答案

I'm reposting my answer from here because the solution should apply to your question as well. It will...

  • not kill the kernel on exit
  • not display a full traceback (no traceback for use in IPython shell)
  • not force you to entrench code with try/excepts
  • work with or without IPython, without changes in code

Just import 'exit' from the code beneath into your jupyter notebook (IPython notebook) and calling 'exit()' should work. It will exit and letting you know that...

 An exception has occurred, use %tb to see the full traceback.


IpyExit

"""
# ipython_exit.py
Allows exit() to work if script is invoked with IPython without
raising NameError Exception. Keeps kernel alive.


Use: import variable 'exit' in target script with
'from ipython_exit import exit'
"""


import sys
from io import StringIO
from IPython import get_ipython




class IpyExit(SystemExit):
"""Exit Exception for IPython.


Exception temporarily redirects stderr to buffer.
"""
def __init__(self):
# print("exiting")  # optionally print some message to stdout, too
# ... or do other stuff before exit
sys.stderr = StringIO()


def __del__(self):
sys.stderr.close()
sys.stderr = sys.__stderr__  # restore from backup




def ipy_exit():
raise IpyExit




if get_ipython():    # ...run with IPython
exit = ipy_exit  # rebind to custom exit
else:
exit = exit      # just make exit importable
小开

To stop current and subsequent cells quietly:

class StopExecution(Exception):
def _render_traceback_(self):
pass


raise StopExecution
小开

Not saying this is a good idea, but you can wrap the start of the cell in a single iteration for loop, then call 'break' to stop further execution.


for _ in range(1):
# do some stuff
if some_condition:
break
小开

A simple answer would be to wrap the code inside a function and use return to stop execution

def func:
if x==y:
return

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