Writing to easygui textbox as function is running?

I don't think there's any simple way of getting EasyGUI's textbox function to do what you want short of modifying the module. Since it's a function not a class, you can't even derive a subclass from it in order to easily reuse its code.

However it's completely feasible to create a separate Tkinter window that just displays lines of text as they are sent to it using an enhanced version of some code I found once in a thread on the comp.lang.python newsgroup.

The original code was designed to catch and display only stderr output from a GUI application which normally doesn't have stderr output handle, so the module was named errorwindow. However I modified it to be able redirect both stderr and stdout to such windows in one easygui-based app I developed, but I never got around to renaming it or updating the comments in it to also mention stdout redirection. ;¬)

Anyway, the module works by defining and creating two instances of a file-like class named OutputPipe when it's imported and assigns them to the sys.stdout and sys.stderr I/O stream file objects which are usually None in a Python .pyw GUI applications (on Windows). When output is first sent to either one of these, the same module is launched as separate Python process with its stdin, stdout, and stderr I/O handles piped with the original process.

There's a lot going on, but if nothing else, with a little study of it might give you some ideas about how to get easygui's textbox to do what you want. Hope this helps.

Note: The code posted is for Python 2.x, there's a modified version that will work in both Python 2 and 3 in my answer to another question, if anyone is interested.

File errorwindow.py:

# Code derived from Bryan Olson's source posted in this related Usenet discussion:
#   https://groups.google.com/d/msg/comp.lang.python/HWPhLhXKUos/TpFeWxEE9nsJ
#   https://groups.google.com/d/msg/comp.lang.python/HWPhLhXKUos/eEHYAl4dH9YJ
#
#   Here's a module to show stderr output from console-less Python
#   apps, and stay out of the way otherwise. I plan to make a ASPN
#   recipe of it, but I thought I'd run it by this group first.
#
#   To use it, import the module. That's it. Upon import it will
#   assign sys.stderr.
#
#   In the normal case, your code is perfect so nothing ever gets
#   written to stderr, and the module won't do much of anything.
#   Upon the first write to stderr, if any, the module will launch a
#   new process, and that process will show the stderr output in a
#   window. The window will live until dismissed; I hate, hate, hate
#   those vanishing-consoles-with-critical-information.
#
#   The code shows some arguably-cool tricks. To fit everthing in
#   one file, the module runs the Python interpreter on itself; it
#   uses the "if __name__ == '__main__'" idiom to behave radically
#   differently upon import versus direct execution. It uses TkInter
#   for the window, but that's in a new process; it does not import
#   TkInter into your application.
#
#   To try it out, save it to a file -- I call it "errorwindow.py" -
#   - and import it into some subsequently-incorrect code. For
#   example:
#
#        import errorwindow
#
#        a = 3 + 1 + nonesuchdefined
#
#   should cause a window to appear, showing the traceback of a
#   Python NameError.
#
#   --
#   --Bryan
#   ----------------------------------------------------------------
#
#   martineau - Modified to use subprocess.Popen instead of the os.popen
#               which has been deprecated since Py 2.6. Changed so it
#               redirects both stdout and stderr. Added numerous
#               comments, and also inserted double quotes around paths
#               in case they have embedded space characters in them, as
#               they did on my Windows system.

"""
    Import this module into graphical Python apps to provide a
    sys.stderr. No functions to call, just import it. It uses
    only facilities in the Python standard distribution.

    If nothing is ever written to stderr, then the module just
    sits there and stays out of your face. Upon write to stderr,
    it launches a new process, piping it error stream. The new
    process throws up a window showing the error messages.
"""
import subprocess
import sys
import thread
import os

if __name__ == '__main__':  # when spawned as separate process
    # create window in which to display output
    # then copy stdin to the window until EOF
    # will happen when output is sent to each OutputPipe created
    from Tkinter import BOTH, END, Frame, Text, TOP, YES
    import tkFont
    import Queue

    queue = Queue.Queue(100)

    def read_stdin(app, bufsize=4096):
        fd = sys.stdin.fileno()  # gets file descriptor
        read = os.read
        put = queue.put
        while True:
            put(read(fd, bufsize))

    class Application(Frame):
        def __init__(self, master=None, font_size=8, text_color='#0000AA', rows=25, cols=100):
            Frame.__init__(self, master)
            # argv[0]: name of this script (not used)
            # argv[1]: name of script that imported this module
            # argv[2]: name of redirected stream (optional)
            if len(sys.argv) < 3:
                title = "Output Stream from %s" % (sys.argv[1],)
            else:
                title = "Output Stream '%s' from %s" % (sys.argv[2], sys.argv[1])
            self.master.title(title)
            self.pack(fill=BOTH, expand=YES)
            font = tkFont.Font(family='Courier', size=font_size)
            width = font.measure(' '*(cols+1))
            height = font.metrics('linespace')*(rows+1)
            self.configure(width=width, height=height)
            self.pack_propagate(0)  # force frame to be configured size
            self.logwidget = Text(self, font=font)
            self.logwidget.pack(side=TOP, fill=BOTH, expand=YES)
            # Disallow key entry, but allow copy with <Control-c>
            self.logwidget.bind('<Key>', lambda x: 'break')
            self.logwidget.bind('<Control-c>', lambda x: None)
            self.logwidget.configure(foreground=text_color)
            #self.logwidget.insert(END, '==== Start of Output Stream ====\n\n')
            #self.logwidget.see(END)
            self.after(200, self.start_thread, ())

        def start_thread(self, _):
            thread.start_new_thread(read_stdin, (self,))
            self.after(200, self.check_q, ())

        def check_q(self, _):
            log = self.logwidget
            log_insert = log.insert
            log_see = log.see
            queue_get_nowait = queue.get_nowait
            go = True
            while go:
                try:
                    data = queue_get_nowait()
                    if not data:
                        data = '[EOF]'
                        go = False
                    log_insert(END, data)
                    log_see(END)
                except Queue.Empty:
                    self.after(200, self.check_q, ())
                    go = False

    app = Application()
    app.mainloop()

else: # when module is first imported
    import traceback
    class OutputPipe(object):
        def __init__(self, name=''):
            self.lock = thread.allocate_lock()
            self.name = name

        def __getattr__(self, attr):
            if attr == 'pipe':  # pipe attribute hasn't been created yet
                # launch this module as a separate process to display any output
                # it receives.
                # Note: It's important to put double quotes around everything in case
                # they have embedded space characters.
                command = '"%s" "%s" "%s" "%s"' % (sys.executable,                # command
                                                   __file__,                      # argv[0]
                                                   os.path.basename(sys.argv[0]), # argv[1]
                                                   self.name)                     # argv[2]

                # sample command and arg values on receiving end:
                #   E:\Program Files\Python\python[w].exe                         # command
                #   H:\PythonLib\TestScripts\PyRemindWrk\errorwindow.py           # argv[0]
                #   errorwindow.py                                                # argv[1]
                #   stderr                                                        # argv[2]

                # execute this script as __main__ with a stdin PIPE for sending output to it
                try:
                    # had to make stdout and stderr PIPEs too, to make it work with pythonw.exe
                    self.pipe = subprocess.Popen(command, bufsize=0,
                                                 stdin=subprocess.PIPE,
                                                 stdout=subprocess.PIPE,
                                                 stderr=subprocess.PIPE).stdin
                except Exception:
                    # output exception info to a file since this module isn't working
                    exc_type, exc_value, exc_traceback = sys.exc_info()
                    msg = ('%r exception in %s\n' %
                            (exc_type.__name__, os.path.basename(__file__)))
                    with open('exc_info.txt', 'wt') as info:
                        info.write('msg:' + msg)
                        traceback.print_exc(file=info)
                    sys.exit('fatal error occurred spawning output process')

            return super(OutputPipe, self).__getattribute__(attr)

        def write(self, data):
            with self.lock:
                self.pipe.write(data)  # 1st reference to pipe attr will cause it to be created

    # redirect standard output streams in the process importing the module
    sys.stderr = OutputPipe('stderr')
    sys.stdout = OutputPipe('stdout')