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I have a Python script, and I want to execute it up to a certain point, then stop, and keep the interpreter open, so I can see the variables it defines, etc.

I know I could generate an exception, or I could invoke the debugger by running pdb.set_trace(), then stop the debugger, which is what I currently use.

...but is there a command that will just stop the script, as if it had simply reached its end? This would be equivalent to commenting the entire rest of the script (but I would not like doing that), or putting an early return statement in a function.

It seems as if something like this has to exist but I have not found it so far.

Edit: Some more details of my usecase

I'm normally using the regular Python consoles in Spyder. IPython seems like a good thing but ( at least for the version I'm currently on, 2.2.5) some of the normal console's features don't work well in IPython (introspection, auto-completion). More often than not, my code generates matplotlib figures. In debug mode, those cannot be updated (to my knowledge), which is why I need to get completely out of the script, but not the interpreter). Another limit of the debugger is that I can't execute loops in it: you can copy/paste the code for a loop into the regular console and have it execute, but that won't work in the debugger (at least in my Spyder version).

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  • 1
    Can't speak for any specific command but PyCharm is a pretty sweet IDE and it lets you do stuff like this. It even lets you evaluate arbitrary expressions on any variables in-scope when you hit a breakpoint. Commented Jan 19, 2017 at 17:33
  • Why not just use pdb and set a breakpoint where you want the code to stop? Commented Jan 19, 2017 at 17:34

3 Answers 3

Reset to default
18

If you invoke your program with python -i <script>, the interpreter will remain active after the script ends. raise SystemExit would be the easiest way to force it to end at an arbitrary point.

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That seems work nicely in IPython, and it works in the regular interpreter if I launch the script in a dedicated instance. If I run it from a previously opened console, it will close the console along with the script. Is there another exception which causes no traceback and won't close the console? All the other exceptions I've tried will keep the console open but cause a traceback. acceptable but not pretty.
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If you have ipython (highly, highly recommended), you can go to any point in your program and add the following lines

import IPython
IPython.embed()

Once your program reaches that point, the embed command will open up a new IPython shell within that context.

I really like to do that for things where I don't want to go the full pdb route.

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4 Comments

I've just tried that and it's nifty, even works when running within a non-IPython console, and I can continue the execution with exit(). -- The problems I found are that matplotlib figures are frozen, as with the debugger, that I cannot query single-letter variables (as in the debugger) by just entering their name and hitting enter, and that if I do run the rest of the script, it seems to drop me in an IPython console, altough it was previously a regular one. -- oh, it does not work when running from an IPython console! No problem for me but should be mentioned.
Huh that's weird, I can use matplotlib without a problem there. And querying variables isn't a problem either.
Inline figures work but all my programs use the QT backend and detached windows. I can update them but will only see the changes once I let the program continue. For variables, I usually use the variable instpector anyway but just define a=5, then simply enter a and hit enter. No reaction in my case, although it works for a_variable=5, and a+2 also works correctly. This may be something in Spyder. Easy to work around but annoying nonetheless.
I use runserver_plus for django, but i was looking for something similar for testing in console also. and this is exactly what i was looking for. Else pdb is painful
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If you are using the Python Shell, just press CTRL + C to throw a KeyboardInterrupt. You can then check out the state of the program at the time the exception was throw.

x = 0
while True:
    x += 1

Running the script...

Python 2.7.6 (default, Nov 10 2013, 19:24:18) [MSC v.1500 32 bit (Intel)] on win32 Type "copyright", "credits" or "license()" for more information. >>> ================================ RESTART ================================

Traceback (most recent call last):

File "C:/Python27/test.py", line 2, in

while True:

KeyboardInterrupt

>>> x

15822387

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