title: pyqt4 how to know textEdit field is empty
body: <p>I want to know if textbox is empty or not. So, I made this code. But, if self.row is ' '  &lt;- this is not working. Although, textEdit field is empty but, it's not recognize.</p>
  
  <pre><code>   def setUi(self):
      self.textEdit = QtGui.QTextEdit(MainWindow) 
      self.textEdit.setGeometry(QtCore.QRect(155, 90, 471, 31))
      self.textEdit.setObjectName(_fromUtf8("textEdit"))
  
  
  
     def bringcolumn(self):
      self.row = self.textEdit.toPlainText() 
  
      if self.row is '': #I want to know if self.row is empty of not.
          QtGui.QMessageBox.information(self, "Message", "ERROR")
  </code></pre>