CODEWITHSUNDEEP
pythonpython-3.xipythonexit
DYZ
DYZ

Reputation: 57033

quit() works differently in Python-3.x and IPython

The built-in function quit() behaves differently in Python-3.x and IPython 3. The following code prints Hello if executed in IPython, but does not print anything in Python:

quit()
print("Hello")

What is the purpose of quit() in IPython? What was the reason for changing its behavior?

Upvotes: 4

Views: 848

Answers (1)

ShadowRanger
ShadowRanger

Reputation: 155363

It looks like IPython's quit/exit "function" simplifies to just setting a flag to say "you should exit when this is next checked". It doesn't raise SystemExit itself, so it's presumably dependent on an intermittent check that, if you queue both commands at once, isn't performed until the second command finishes.

You can check it yourself at the IPython prompt, first run quit?? to see that it's a callable class whose __call__ delegates to self._ip.ask_exit(). Next, run quit._ip.ask_exit?? and you'll see that ask_exit just sets a flag, self.exit_now = True (and it's a plain attribute if you check it, not a property with hidden code execution).

You're welcome to track down where IPython is checking that; I'm guessing it's done after any given line or cell of IPython completes.

Fundamentally, the difference is that quit in IPython has never been the same as quit in regular Python's interactive interpeter; quit/exit as a built-in is intended to be replaced for alternate interactive interpreters, and needn't behave exactly the same. If you want a consistent exit behavior, import sys and run sys.exit(), which is also the correct way to exit early inside a script, and is not intended as a hook for the interactive prompt.

Upvotes: 6

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