def center_widget_on_screen(widget, screen=None):
    """
    Centers given Widget on the screen.

    :param widget: Current Widget.
    :type widget: QWidget
    :param screen: Screen used for centering.
    :type screen: int
    :return: Definition success.
    :rtype: bool
    """

    screen = screen and screen or QApplication.desktop().primaryScreen()
    desktop_width = QApplication.desktop().screenGeometry(screen).width()
    desktop_height = QApplication.desktop().screenGeometry(screen).height()
    widget.move(desktop_width / 2 - widget.sizeHint().width() / 2, desktop_height / 2 - widget.sizeHint().height() / 2)
    return True