#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import random
import io
import sys
import os
import time

from PyQt4.QtGui import *
from PyQt4.QtCore import *
from PyQt4.uic import *

""" MainWindow class """
class Main(QMainWindow):
    def __init__(self, parent = None):
        super(Main, self).__init__(parent)

        # arquivo da interface
        loadUi('MainWindow.ui', self)

        ...

        self.edtTexto.setText('')

        ...

if __name__ == "__main__":
    app = QApplication(sys.argv)

    darks_w = Main()
    darks_w.setWindowTitle('Teste')
    darks_w.show()

    sys.exit(app.exec_())