30combo.py

#! /usr/bin/python
# -*- coding: utf-8 -*-

import sys
from PyQt5.QtWidgets import QApplication, QWidget, QLabel, QComboBox


class Myform(QWidget):

    def __init__(self):

        super(Myform, self).__init__()

        self.initUI()

    def initUI(self):

        self.lbl = QLabel("Ubuntu", self)

        combo = QComboBox(self)
        combo.addItem("Ubuntu")
        combo.addItem("Mandrive")
        combo.addItem("Fedora")
        combo.addItem("Arch")
        combo.addItem("Gentoo")

        combo.move(50, 50)
        self.lbl.move(50, 150)

        combo.activated[str].connect(self.onActivated)

        self.setGeometry(300, 300, 300, 200)
        self.setWindowTitle('combobox')
        self.show()

    def onActivated(self, text):

        self.lbl.setText(text)
        self.lbl.adjustSize()

if __name__ == '__main__':

    app = QApplication(sys.argv)
    w = Myform()
    sys.exit(app.exec_())