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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 exit_if_missing_graphviz(self):
 """ Detect the presence of the dot utility to make a png graph. """

        (out, err) = utils.capture_shell("which dot")

        if "dot" not in out:
            ui.error(c.MESSAGES["dot_missing"])