def onActivated():
  s=combo.currentText()
  print(s)

  comb = QComboBox(root)
  comb.addItems(["Ubuntu", "Mandriva", "Fedora", "Arch", "Gentoo"])

  comb.move(50, 250)
  comb.activated[str].connect(onActivated)
btn = QPushButton('Button',root)
btn.resize(100,30)
btn.clicked.connect(onActivated)
btn.move(50, 50)