(Python) Append text dynamically in multi-threaded IRC GUI
Question: I'm writing a simple IRC server and client GUI using wxPython. In my
application, I had two threads running: One for the GUI, and one for the
socket connections required to send and receive information. So far, I believe
that I am successfully connecting to the server with the client application,
but I am seeing no messages processed. I tried using my client with another
TCP listener application and I was able to send a message successfully. I
believe the problem lies in the way I have set up the GUI. Here is my code for
the serverside application (apologies for any awkward spacing)

I have a feeling the problem lies within the bootUp() function..

    
    
    #!/usr/bin/python
    
    import wx
    import socket
    import threading
    from threading import Thread
    
    ip = ""
    port = 0
    backlog = 5
    
    chatText = ""
    
    class relayServerGUI(wx.Frame):
    def __init__(self, parent, id):
        wx.Frame.__init__(self, parent, id, "Enter IP address", size = (600, 600))
        orciPanel = wx.Panel(self)
        relayChat = wx.TextCtrl(orciPanel, 0, chatText, (50, 50), (500, 500),style              = wx.TE_MULTILINE)
        portInput = wx.TextEntryDialog(None, "Enter Port: ", "")
        if portInput.ShowModal() == wx.ID_OK:
            global port
            port = int(portInput.GetValue())
            thread2()       
    
    def relayInterpretor():
        socketRelay = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        socketRelay.bind((ip, port))
        socketRelay.listen(backlog)
        client, address = socketRelay.accept()
    
        while 1:
                        relayData = client.recv(1024)
                        global chatText
                        chatText += (relayData)
                        client.send(relayData)
    
    
    def bootUP():
    if __name__ == "__main__":
        relayApplication = wx.PySimpleApp()
        relayFrame = relayServerGUI(parent = None, id = -1)
        relayFrame.Show()
        relayApplication.MainLoop()
    
        while 1:
            relayChat.Clear()
            relayChat.AppendText(chatText)
    
    Thread(target = bootUP).start()
    def thread2():
        Thread(target = relayInterpretor).start()
    

EDIT: relayChat is where the messages would, ideally, be displayed. I set it
to copy chatText, a global string variable so I would not have to delve into
cross-threading.


Answer: I am not very fluent in wx, but I think this problem isn't very specifically
wx related anyways. I see two possible issues here.

First, you are sharing a string between threads to communicate text to the
`relayChat` widget, which is usually a very bad approach. There should be a
way for your to emit an event in wx from the thread, so that the event loop
will pick it up in the main thread and run a handler that updates the widget.

Secondly, the event loop...

    
    
    relayApplication.MainLoop()
    

That is a blocking call. Your application enters the event loop, so this
following code is not getting executed:

    
    
    while 1:
        relayChat.Clear()
        relayChat.AppendText(chatText)
    

Again, this ties back into the first point. When the socket in the thread
receives some data, it should be emitting an event with that data, so the main
gui thread can properly call a handler that will append to your widget.

**Update**

Referencing [this
question](http://stackoverflow.com/questions/2345608/wxpython-threading-gui-
using-custom-event-handler) on how to emit custom wx events, you could
probably fix it like this:

    
    
    from wx.lib.newevent import NewEvent
    
    ChatTextEvent, EVT_CHATTEXT = NewEvent()
    
    class relayServerGUI(wx.Frame):
        def __init__(self, parent, id):
            ...
            # make sure to save a ref to your chat widget
            self.relayChat = wx.TextCtrl(orciPanel, 0, chatText, (50, 50), (500, 500),style              = wx.TE_MULTILINE)
            self.Bind(EVT_CHATTEXT, self.newChatTextEvent)
            ...
            thread2(self)
    
        def newChatTextEvent(self, event):
            self.relayChat.AppendText(event.data)
    
    
    def relayInterpretor(wxObject):
       ...
       while 1:
          ...
          # wxObject needs to be an instance of relayServerGUI
          wx.PostEvent(wxObject, ChatTextEvent(data=relayData))
    
    def thread2(wxObject):
        Thread(target = relayInterpretor, args=(wxObject,)).start()    
    

*Note: I am not 100% on that syntax. Try it out. It may need a slight tweak.

