'If themename is None, returns the theme in use, otherwise, set
the current theme to themename, refreshes all widgets and emits
a <<ThemeChanged>> event.'

def theme_use(self, themename=None):

    if (themename is None):
        return self.tk.eval('return    $ttk::currentTheme')
    else:
        self.tk.call('ttk::setTheme', themename)
        return
