CODEWITHSUNDEEP
pythonpython-3.x
Amateur_C_Man
Amateur_C_Man

Reputation: 9

If I Keyboard Interupt a running Python script, is there a way to begin again where it left off? (windows)

I have a long-running script at work (windows unfortunately) where I programmed it to print the current analysis results if I ctrl-c. However, I was curious if after doing ctrl-c, I could start the script running again where it left off?

This is actually 3 questions: -is it possible to do this without any programming changes? - e.g. I accidentally hit ctrl-c and want to retroactively start it where it left off -can I use a command like ctrl-z (only on Mac I believe) on windows and program the script to print results when I issue it? -what is the best programmatic way of automatically finishing the execution of the line I am on (massive .txt file of data) when I use an interrupt command, store that line number (in a file maybe), and restart the program on the next line with the next execution?

Thanks!

(FYI: I'm a novice Pythoner and my script currently takes about 10 min to perform 1 million lines. Files I will use in the future will often have 100+ million lines)

Upvotes: 0

Views: 51

Answers (1)

BoarGules
BoarGules

Reputation: 16942

The short answer to your first question is No. Ctrl-C signals the interpreter, which unwinds the stack, presents you with a stack trace, and halts. You can't recover from ctrl-C for the same reason that you can't recover from any other untrapped exception. What you are asking for is a quick way to put Humpty Dumpty back together again.

You can restart a chess game from any point simply by laying out the pieces according to a picture you made before abandoning the game. But you can't easily do that with a program. The problem is that knowing the line number where the program stopped is not nearly enough information to recreate the state of the program at the time: the values of all the variables, the state of the stack, how much of the input it had read, and so forth. In other words, the picture is complicated, and laying out the pieces accurately is hard.

If your program is writing to the Windows console, you can suspend output by pressing ctrl-S and restart it by pressing ctrl-Q. These control characters are holdovers from the days of Teletype machines, but modern terminal emulators still obey them. This is a quick way to do what you want without program changes. Unsophisticated, but maybe good enough to begin with.

And your program will probably run a lot faster if it writes its output to file, for later examination in a text editor, rather than writing directly to the Windows console.

A full-on solution to your problem is something that I hesitate to recommend to a novice. The idea is to split calculation and display into two processes. The calculation process does its thing and feeds its results line by line to the display process. The display process listens to the calculation process and puts the results that it gets on the screen, but can also accept pause and resume commands. What happens while it is in the paused state is a design decision. You can decide either that the calculation process should block (easier option) or that it should buffer its results until the display process is ready to accept them again (harder option).

Upvotes: 1

Related Questions