How to control/call another python script within one python script? (Communicate between scripts)

Question

I'm working on one GUI program, and was gonna add a long running task into one event, but I found this would make the whole program freeze a lot, so considering other people's advice I would make the GUI only responsible for starting, stopping and monitoring and make the long running task run as a separate script. The only way I know to run another script in one script is by import, is there any other methods to communicate with another script, I mean such as reading another's stdout and terminating it at any time you want?

Answer 1

If communicating by stdin/stdout is what you need, you should use the subprocess module.

Answer 2

There is much better way to do that, than reading stdout: http://docs.python.org/library/multiprocessing.html

Answer 3

I suggest you look at the threading module. By subclassing the Thread class you can create new threads for time intensive jobs.

Then for communication between the the threads you can use either pubsub or pydispatcher, I haven't tried the latter so I can't comment on it but I would recommend pubsub for its ease of use and the fact that its apart of wxpython is a bonus.

Here is a wxpython wiki page on running long tasks, skip to the end if you want the simplest example usage of threading.

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Heres a simple (runnable) example of how you could use pubsub to send messages from your workerThread to your GUI.

import time

import wx
from threading import Thread
from wx.lib.pubsub import Publisher

class WorkerThread(Thread):
    def __init__(self):
        Thread.__init__(self)

        #A flag that can be set 
        #to tell the thread to end
        self.stop_flag = False

        #This calls the run() to start the new thread
        self.start()


    def run(self):
        """ Over-rides the super-classes run()"""
        #Put everything in here that 
        #you want to run in your new thread

        #e.g...
        for x in range(20):
            if self.stop_flag:
                break
            time.sleep(1)
            #Broadcast a message to who ever's listening
            Publisher.sendMessage("your_topic_name", x)
        Publisher.sendMessage("your_topic_name", "finished")


    def stop(self):
        """
        Call this method to tell the thread to stop
        """
        self.stop_flag = True




class GUI(wx.Frame):
    def __init__(self, parent, id=-1,title=""):
        wx.Frame.__init__(self, parent, id, title, size=(140,180))
        self.SetMinSize((140,180)) 
        panel = wx.Panel(id=wx.ID_ANY, name=u'mainPanel', parent=self)

        #Subscribe to messages from the workerThread
        Publisher().subscribe(self.your_message_handler, "your_topic_name")

        #A button to start the workerThread
        self.startButton = wx.Button(panel, wx.ID_ANY, 'Start thread')
        self.Bind(wx.EVT_BUTTON,  self.onStart, self.startButton)

        #A button to stop the workerThread
        self.stopButton = wx.Button(panel, wx.ID_ANY, 'Stop thread')
        self.Bind(wx.EVT_BUTTON,  self.onStop, self.stopButton)

        #A text control to display messages from the worker thread
        self.threadMessage = wx.TextCtrl(panel, wx.ID_ANY, '', size=(75, 20))

        #Do the layout
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(self.startButton, 0, wx.ALL, 10)
        sizer.Add(self.stopButton, 0, wx.ALL, 10)
        sizer.Add(self.threadMessage, 0, wx.ALL, 10)
        panel.SetSizerAndFit(sizer)


    def onStart(self, event):
        #Start the worker thread
        self.worker = WorkerThread()

        #Disable any widgets which could affect your thread
        self.startButton.Disable()

    def onStop(self, message):
        self.worker.stop()

    def your_message_handler(self, message):
        message_data = message.data
        if message_data == 'finished':
            self.startButton.Enable()
            self.threadMessage.SetLabel(str(message_data))
        else:
            self.threadMessage.SetLabel(str(message_data))

if __name__ == "__main__":

    app = wx.PySimpleApp()
    frame = GUI(None, wx.ID_ANY, 'Threading Example')
    frame.Show()
    app.MainLoop()