Getting Out of The Python's Loops

Python is a great language - I used it many times for measurement automation. The only thing I stumbled on from time to time was a simple control over long time or infinite loops. When the loop is running it should check for a key or a button been pressed without stopping and waiting for input. Such stopping and waiting happens, for example, when a function like getch() is used.

The case in general looks like this:

while 1:
   print 1,

and the problem is how to get out of the loop gracefully without killing the program.

I'm aware of the following variants to deal with the situation:

1. Ctrl-C/Crtl-D keyboard program termination. It works but kills whole program. It is possible to avoid that by exception processing of the error:

   try:
      while 1:
          print 1,
   # on ctrl-d or ctrl-c
   except (EOFError, KeyboardInterrupt):
      print '\n exception handled'
   print 'Clean Exit on Ctrl-C/D'



2. Tkinter - it allows to stop looping on event as "button pressed":

   import time
   from Tkinter import *
   
   class App:
     
      Var = 1
   
      def __init__(self, master):
          frame = Frame(master)
          frame.pack()
   
          self.button = Button(frame, text="QUIT",
                               command=frame.quit)
          self.button.pack(side=LEFT)
   
          self.stoploop = Button(frame, text="Stop",
                                 command=self.stopLoop)
          self.stoploop.pack(side=LEFT)
                 
          while self.Var == 1:
              time.sleep(1)
              print self.Var,
   
          print "\nClean exit from the loop"
   
      def stopLoop(self):
          self.Var = 0
          print "Var = %d" % self.Var
   
   root = Tk()
   app = App(root)
   root.mainloop()



3. Loop in a separate thread (similar to Tkinter variant) - I came up with this idea before finding other better solutions: if the loop is running in a separate thread then user still has access to the main program from keyboard and hence can control the loop too:

   import threading, time
   
   class LoopThread (threading.Thread):
   
     Value = 0
     Counts = 0
   
     def run(self):
        print 'Loop is started'
        while self.Value != 10:
           time.sleep(1)
           self.Counts = self.Counts + 1
        print 'Loop was ended, Counts %d' % self.Counts
    
     def getVal(self):
        return self.Value
   
     def setVal(self, Val):
        self.Value = Val
   
   # Create the object
   MyLoop = LoopThread()
   
   # Start the thread
   MyLoop.start()
   
   # Send the loop termination value from
   # the main program whenever you need
   time.sleep(11)
   MyLoop.setVal(10)

   A disadvantage of this approach is that the loop thread can not use the terminal window since the main program needs it for input from a user. If it is about logging information in the loop - then the info should be saved into a file, for example.

If you know any other solutions - please, share your experience.