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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 close(self):
 """Close the canvas Notes ----- This will usually destroy the GL context. For Qt, the context (and widget) will be destroyed only if the widget is top-level. To avoid having the widget destroyed (more like standard Qt behavior), consider making the widget a sub-widget. """

        if self._backend is not None and not self._closed:
            self._closed = True
            self.events.close()
            self._backend._vispy_close()
        forget_canvas(self)