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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 start_virtual_display(self, width=1440, height=900, colordepth=24, **kwargs):
 """Starts virtual display which will be destroyed after test execution will be end *Arguments:* - width: a width to be set in pixels - height: a height to be set in pixels - color_depth: a color depth to be used - kwargs: extra parameters *Example:* | Start Virtual Display | | Start Virtual Display | 1920 | 1080 | | Start Virtual Display | ${1920} | ${1080} | ${16} | """

        if self._display is None:
            logger.info("Using virtual display: '{0}x{1}x{2}'".format(
                        width, height, colordepth))

            self._display = Xvfb(int(width), int(height),
                                 int(colordepth), **kwargs)
            self._display.start()
            atexit.register(self._display.stop)