Re: Catching control-C
On Jul 9, 7:28 pm, Miles Kaufmann mile...@umich.edu wrote: On Jul 9, 2009, at 9:20 AM, Lie Ryan wrote: Michael Mossey wrote: I want to understand better what the secret is to responding to a ctrl-C in any shape or form. Are you asking: when would the python interpreter process KeyboardInterrupt? ... In single threaded python program, the currently running thread is always the main thread (which can handle KeyboardInterrupt). I believe SIGINT is checked at every ticks. But SIGINT cannot interrupt atomic operations (i.e. it cannot interrupt long operations that takes a single tick). Some otherwise atomic single-bytecode operations (like large integer arithmetic) do manual checks for whether signals were raised (though that won't help at all if the operation isn't on the main thread). I believe a tick in python is equivalent to a single bytecode, but please correct me if I'm wrong. Not all opcodes qualify as a tick. In general, those opcodes that cause control to remain in the eval loop (and not make calls to other Python or C functions) don't qualify as ticks (but there are exceptions, e.g. so that while True: pass is interruptible). In Python/ceval.c: PyEval_EvalFrameEx(), those opcodes that don't end in goto fast_next_opcode are ticks. Please correct me if _I'm_ wrong! :) -Miles You don't need to do I/O. This works: try: process_forever() except KeyboardInterrupt: save critical stuff write nice messages I often wrap a large computational task like this, with the idea that the exception can let me exit safely, in my case by writing restart parameters and printing a summary pf progress to date. Gerry -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
Michael Mossey wrote: On Jul 6, 2:47 pm, Philip Semanchuk phi...@semanchuk.com wrote: On Jul 6, 2009, at 5:37 PM, Michael Mossey wrote: What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. You can use a try/except to catch a KeyboardInterrupt exception, or you can trap it using the signal module:http://docs.python.org/library/signal.html You want to trap SIGINT. HTH Philip Thanks to both of you. However, my question is also about whether I need to be doing i/o or some similar operation for my program to notice in any shape or form that Control-C has been pressed. In the past, I've written Python programs that go about their business ignoring Ctrl-C. Other programs respond to it immediately by exiting. I think the difference is that the latter programs are doing i/o. But I want to understand better what the secret is to responding to a ctrl-C in any shape or form. For example, does trapping SIGINT always work, regardless of what my process is doing? Thanks, Mike Are you asking: when would the python interpreter process KeyboardInterrupt? In a multi threaded python program (where KeyboardInterrupt doesn't always work), only the main thread can process KeyboardInterrupt; thus the main thread must regain control before the interrupt is raised. Normally, python will context switch (i.e. thread switch) every 100 interpreter ticks, but when the interpreter received a SIGINT, the interpreter will try to context switch as fast as it can (every tick) to allow the main thread to regain control. So the answer is in multithreaded python program: when the main thread regains control In single threaded python program, the currently running thread is always the main thread (which can handle KeyboardInterrupt). I believe SIGINT is checked at every ticks. But SIGINT cannot interrupt atomic operations (i.e. it cannot interrupt long operations that takes a single tick). An example, where python have difficulties processing KeyboardInterrupt: print 'foo'*1000 ...foofoofoo... because printing a string is an atomic operation I believe a tick in python is equivalent to a single bytecode, but please correct me if I'm wrong. -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
On Jul 9, 2009, at 9:20 AM, Lie Ryan wrote: Michael Mossey wrote: I want to understand better what the secret is to responding to a ctrl-C in any shape or form. Are you asking: when would the python interpreter process KeyboardInterrupt? ... In single threaded python program, the currently running thread is always the main thread (which can handle KeyboardInterrupt). I believe SIGINT is checked at every ticks. But SIGINT cannot interrupt atomic operations (i.e. it cannot interrupt long operations that takes a single tick). Some otherwise atomic single-bytecode operations (like large integer arithmetic) do manual checks for whether signals were raised (though that won't help at all if the operation isn't on the main thread). I believe a tick in python is equivalent to a single bytecode, but please correct me if I'm wrong. Not all opcodes qualify as a tick. In general, those opcodes that cause control to remain in the eval loop (and not make calls to other Python or C functions) don't qualify as ticks (but there are exceptions, e.g. so that while True: pass is interruptible). In Python/ceval.c: PyEval_EvalFrameEx(), those opcodes that don't end in goto fast_next_opcode are ticks. Please correct me if _I'm_ wrong! :) -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
Steven D'Aprano st...@remove-this-cybersource.com.au wrote: On Mon, 06 Jul 2009 15:02:26 -0700, Michael Mossey wrote: On Jul 6, 2:47 pm, Philip Semanchuk phi...@semanchuk.com wrote: On Jul 6, 2009, at 5:37 PM, Michael Mossey wrote: What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. You can use a try/except to catch a KeyboardInterrupt exception, or you can trap it using the signal module:http://docs.python.org/library/signal.html You want to trap SIGINT. HTH Philip Thanks to both of you. However, my question is also about whether I need to be doing i/o or some similar operation for my program to notice in any shape or form that Control-C has been pressed. In the past, I've written Python programs that go about their business ignoring Ctrl-C. I bet that somewhere in your code you have something like: for x in really_big_list: try: long_running_process(x) except: continue If that's what you're doing, stop! The correct way is: for x in really_big_list: try: long_running_process(x) except Exception: # Let KeyboardInterrupt and SystemExit through. continue Note that it is a relatively recent change (in python 2.5) which made KeyboardInterrupt not a child of Exception n...@dogger:~$ python2.4 Python 2.4.6 (#2, Feb 17 2009, 20:01:48) [GCC 4.3.3] on linux2 Type help, copyright, credits or license for more information. Loaded customisations from '/home/ncw/.pystartup' isinstance(KeyboardInterrupt(), Exception) True n...@dogger:~$ python2.5 Python 2.5.4 (r254:67916, Feb 17 2009, 20:16:45) [GCC 4.3.3] on linux2 Type help, copyright, credits or license for more information. Loaded customisations from '/home/ncw/.pystartup' isinstance(KeyboardInterrupt(), Exception) False for x in really_big_list: try: long_running_process(x) except (KeyboardInterrupt, SystemExit): print User requested exit... shutting down now cleanup() raise except Exception: continue That is the backwards compatible way -- Nick Craig-Wood n...@craig-wood.com -- http://www.craig-wood.com/nick -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
On Jul 6, 6:02 pm, Michael Mossey michaelmos...@gmail.com wrote: On Jul 6, 2:47 pm, Philip Semanchuk phi...@semanchuk.com wrote: On Jul 6, 2009, at 5:37 PM, Michael Mossey wrote: What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. You can use a try/except to catch a KeyboardInterrupt exception, or you can trap it using the signal module:http://docs.python.org/library/signal.html You want to trap SIGINT. HTH Philip Thanks to both of you. However, my question is also about whether I need to be doing i/o or some similar operation for my program to notice in any shape or form that Control-C has been pressed. In the past, I've written Python programs that go about their business ignoring Ctrl-C. Other programs respond to it immediately by exiting. I think the difference is that the latter programs are doing i/o. But I want to understand better what the secret is to responding to a ctrl-C in any shape or form. For example, does trapping SIGINT always work, regardless of what my process is doing? Thanks, Mike Try some experiments. ;] -- http://mail.python.org/mailman/listinfo/python-list
Catching control-C
What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. Thanks, Mike -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
On Mon, Jul 6, 2009 at 2:37 PM, Michael Mosseymichaelmos...@gmail.com wrote: What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. try: #code that reads input except KeyboardInterrupt: #Ctrl-C was pressed Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
On Jul 6, 2009, at 5:37 PM, Michael Mossey wrote: What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. You can use a try/except to catch a KeyboardInterrupt exception, or you can trap it using the signal module: http://docs.python.org/library/signal.html You want to trap SIGINT. HTH Philip -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
On Jul 6, 2:47 pm, Philip Semanchuk phi...@semanchuk.com wrote: On Jul 6, 2009, at 5:37 PM, Michael Mossey wrote: What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. You can use a try/except to catch a KeyboardInterrupt exception, or you can trap it using the signal module:http://docs.python.org/library/signal.html You want to trap SIGINT. HTH Philip Thanks to both of you. However, my question is also about whether I need to be doing i/o or some similar operation for my program to notice in any shape or form that Control-C has been pressed. In the past, I've written Python programs that go about their business ignoring Ctrl-C. Other programs respond to it immediately by exiting. I think the difference is that the latter programs are doing i/o. But I want to understand better what the secret is to responding to a ctrl-C in any shape or form. For example, does trapping SIGINT always work, regardless of what my process is doing? Thanks, Mike -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
On Jul 6, 2009, at 6:02 PM, Michael Mossey wrote: On Jul 6, 2:47 pm, Philip Semanchuk phi...@semanchuk.com wrote: On Jul 6, 2009, at 5:37 PM, Michael Mossey wrote: What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. You can use a try/except to catch a KeyboardInterrupt exception, or you can trap it using the signal module:http://docs.python.org/library/signal.html You want to trap SIGINT. HTH Philip Thanks to both of you. However, my question is also about whether I need to be doing i/o or some similar operation for my program to notice in any shape or form that Control-C has been pressed. In the past, I've written Python programs that go about their business ignoring Ctrl-C. Other programs respond to it immediately by exiting. I think the difference is that the latter programs are doing i/o. But I want to understand better what the secret is to responding to a ctrl-C in any shape or form. For example, does trapping SIGINT always work, regardless of what my process is doing? Hi Mike, Sorry, I don't know the Python internals well enough to answer your question. Good luck Philip -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
Michael Mossey wrote: On Jul 6, 2:47 pm, Philip Semanchuk phi...@semanchuk.com wrote: On Jul 6, 2009, at 5:37 PM, Michael Mossey wrote: What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. You can use a try/except to catch a KeyboardInterrupt exception, or you can trap it using the signal module:http://docs.python.org/library/signal.html You want to trap SIGINT. HTH Philip Thanks to both of you. However, my question is also about whether I need to be doing i/o or some similar operation for my program to notice in any shape or form that Control-C has been pressed. You don't need to be doing I/O in order to raise a KeyboardIneterrupt. For example, the following program should use up a lot of your CPU until you hit Ctrl-C. while True: ... pass ... ^CTraceback (most recent call last): File stdin, line 1, in module KeyboardInterrupt In the past, I've written Python programs that go about their business ignoring Ctrl-C. Can you be more specific? Can you share the relevant sections of these programs? Were these programs multi-threaded? But I want to understand better what the secret is to responding to a ctrl-C in any shape or form. Strictly speaking, I don't think you can always respond to a Ctrl-C in any shape or form. Quoting from the signal module: Although Python signal handlers are called asynchronously as far as the Python user is concerned, they can only occur between the atomic instructions of the Python interpreter. This means that signals arriving during long calculations implemented purely in C (such as regular expression matches on large bodies of text) may be delayed for an arbitrary amount of time. HTH, Ben -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
Philip Semanchuk phi...@semanchuk.com (PS) wrote: PS On Jul 6, 2009, at 5:37 PM, Michael Mossey wrote: What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. PS You can use a try/except to catch a KeyboardInterrupt exception, or you PS can trap it using the signal module: PS http://docs.python.org/library/signal.html PS You want to trap SIGINT. And make sure threads don't mess up the signal handling. -- Piet van Oostrum p...@cs.uu.nl URL: http://pietvanoostrum.com [PGP 8DAE142BE17999C4] Private email: p...@vanoostrum.org -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
On Mon, 06 Jul 2009 15:02:26 -0700, Michael Mossey wrote: On Jul 6, 2:47 pm, Philip Semanchuk phi...@semanchuk.com wrote: On Jul 6, 2009, at 5:37 PM, Michael Mossey wrote: What is required in a python program to make sure it catches a control- c on the command-line? Do some i/o? The OS here is Linux. You can use a try/except to catch a KeyboardInterrupt exception, or you can trap it using the signal module:http://docs.python.org/library/signal.html You want to trap SIGINT. HTH Philip Thanks to both of you. However, my question is also about whether I need to be doing i/o or some similar operation for my program to notice in any shape or form that Control-C has been pressed. In the past, I've written Python programs that go about their business ignoring Ctrl-C. I bet that somewhere in your code you have something like: for x in really_big_list: try: long_running_process(x) except: continue If that's what you're doing, stop! The correct way is: for x in really_big_list: try: long_running_process(x) except Exception: # Let KeyboardInterrupt and SystemExit through. continue or even: for x in really_big_list: try: long_running_process(x) except (KeyboardInterrupt, SystemExit): print User requested exit... shutting down now cleanup() raise except Exception: continue -- Steven -- http://mail.python.org/mailman/listinfo/python-list
