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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _apply_base_theme(app):
 """ Apply base theme to the application. Args: app (QApplication):
 QApplication instance. """


    if QT_VERSION < (5,):
        app.setStyle('plastique')
    else:
        app.setStyle('Fusion')

    with open(_STYLESHEET) as stylesheet:
        app.setStyleSheet(stylesheet.read())