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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 callback(self, sources):
 """When a source is selected, enable widgets that depend on that condition and do done_callback"""

        enable = bool(sources)
        if not enable:
            self.plot_widget.value = False
        enable_widget(self.plot_widget, enable)

        if self.done_callback:
            self.done_callback(sources)