RealTime output from a subprogram to a pyQT4 Widget - python-2.7

Question

I'm trying to redirect the stdout from a subprogram to the QTextBrowser widget. (Python 2.7, Window 7, pyQT4)
This is the sub program, it will be in an executable file:
#test.py
import time
print ("ABC")
time.sleep(1)
print ("DEF")
time.sleep(1)
print ("GHI")
time.sleep(1)
print ("JKL")
My pyQT4 program:
from PyQt4 import QtGui
import subprocess, time, os, sys
from subprocess import Popen, PIPE
class GUI (QtGui.QWidget):
def __init__(self):
...
self.initUI()
def initUI(self):
...
self.edit = QtGui.QTextBrowser()
grid.addWidget (self.edit, 7, 0, 5, 7)
def run(self):
p = Popen (['C:\\...\\test.exe'], stdout=PIPE, stderr=subprocess.STDOUT)
while True:
line = p.stdout.readline()
if not line:
break
self.append_edit('>>>' + line)
def append_edit(self, string):
self.edit.append(string)
def main():
app = QtGui.QApplication(sys.argv)
upgrade = GUI()
sys.exit (app.exec_())
The program I have above will wait until the subprogram finish running then print everything into the widget. What I want is for the program to output ABC then DEF so on with one second in between into the widget WHILE the subprogram is running.
Edit: I can have the subprocess output to cmd just fine, however, if I were print it into the QTextBrowser, it will not work.
I have seen many questions about this issue, but none of them seems to answer my question.
Thanks in advance.
Edit: I'm still new to python. I think this is maybe the problem: Fixed by adding QtGui.QApplication.processEvents()
def initUI(self):
...
running = QtGui.QPushButton('Run')
running.clicked.connect(self.run)
def run(self):
time.sleep(1)
append_edit('Before')
time.sleep(2)
append_edit('After')
So when I hit run in my program, instead of printing out Before first then wait 1 sec, it wait 3 seconds in total then print both Before and After. What cause this problem?
Edit: Even with QtGui.QApplication.processEvents() in my code, I'm still having the same issue. it will run the whole subprogram before showing the output to QTextBrowser.