Segfault trying to access gui (single thread)

[alexandernst]

I have a problem trying to hide/show my widget.
This is an example of what I have:

main.py

class Main(QMainWindow):
  def __init__(self):
    QMainWindow.__init__(self, parent=None)
    self.gui = Gui()
 
  def onMyCustomEvent(self):
    self.gui.showOrHide()     #<----  SEGFAULT
 
app = QtGui.QApplication(sys.argv)
window = Main()
sys.exit(app.exec_())

class Main(QMainWindow):
  def __init__(self):
    QMainWindow.__init__(self, parent=None)
    self.gui = Gui()

  def onMyCustomEvent(self):
    self.gui.showOrHide()     #<----  SEGFAULT

app = QtGui.QApplication(sys.argv)
window = Main()
sys.exit(app.exec_())

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gui.py

class Gui(QWidget):
  def __init__(self):
    QWidget.__init__(self, parent=None)
    #set size of widget
    #set title
    #.....
    #.....
 
  def showOrHide(self):
    if self.isVisible():
      self.setVisible(False)
    else:
      self.setVisible(True)

class Gui(QWidget):
  def __init__(self):
    QWidget.__init__(self, parent=None)
    #set size of widget
    #set title
    #.....
    #.....

  def showOrHide(self):
    if self.isVisible():
      self.setVisible(False)
    else:
      self.setVisible(True)

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So, this is the code, and when I try to show or hide the gui, I get a SEGFAULT or a message saying "QCoreApplication::sendPostedEvents: Cannot send posted events for objects in another thread". The SEGFAULT and the message appear randomly.
I have searched and the message means that I must use processEvent, postEvent and so on because I'm trying to access a gui from another thread, but I'm _not_! I don't use threads in my app, so I'm a little confused.
Why could be happening?

Thanks