用户输入打破无限循环？

Question

I'm working on calculating a bunch of triangles with special properties for a Number Theorist friend. There are infinitely many of these triangles, but they require a lot of computational power to find.

We've got an infinite loop running through different b,d combinations. When the program ends, it calls the go(dict) function to export the triangles it found. Currently, we tell the program at the start what interval of time to run for. This is causing problems when we realize we need the computing power for something else, but the program still has hours to run and we don't want to lose the triangles it has already calculated by exiting the program without running go(dict).

Ideally, we want some user input to cause the program to break the loop, run go(dict) with whatever current version of the dictionary it is holding in memory, then exit. Trying with atexit.register(go, dict) was unsuccessful, as it is called many times within the loop and runs many times when the program is terminated.

(See the abbreviated loop code below)

interval = eval(input("How many hours shall I run for? "))*3600
starttime = time.time()
dict = {}
b = start_value
while True:
    for d in range (1, b):
        compute stuff

        if (condition):
            add triangle to dict

    if (time.time()-starttime)>interval:
        go(dict)
        return
    b +=1

Answer 1

This is what exceptions are can be used for: you press Ctrl+C to interrupt the process, and your code handles it by saving the results:

while True:
    try:
        # your code here
    except KeyboardInterrupt:
        go(dict)
        break

Note that you can't return from a standalone loop, but you can break from it, however.

Answer 2

one thing you can do is take over ctrl+c using except KeyboardInterrupt: when you send an interrupt to the script it will run this block in which you can put code to exit cleanly here is an example:

i = 0
try:
    while True:
        i+=1
except KeyboardInterrupt:
    print 'caught INT'
    print i

Answer 3

Using Signals:

import signal
interrupted = False # Used to break the loop when we send SIGINT

# When SIGINT is received, set interrupted to True
def signal_handler(signal, frame):
    global interrupted
    interrupted = True

# Sets signal_handler to run if a SIGINT was received
signal.signal(signal.SIGINT, signal_handler)

interval = eval(input("How many hours shall I run for? "))*3600
starttime = time.time()
dict = {}
b = start_value
while True:
    for d in range (1, b):
        compute stuff

        if (condition):
            add triangle to dict

        if (time.time()-starttime)>interval:
            go(dict)
            break

        if interrupted:
            go(dict)
            break
    b +=1

Now when we hit ctrl+c , we set interrupted to True which runs go(dict) and breaks the loop.