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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 plot_dot_graph(graph, filename=None):
 """ Plots a graph in graphviz dot notation. :param graph: the dot notation graph :type graph: str :param filename: the (optional) file to save the generated plot to. The extension determines the file format. :type filename: str """

    if not plot.pygraphviz_available:
        logger.error("Pygraphviz is not installed, cannot generate graph plot!")
        return
    if not plot.PIL_available:
        logger.error("PIL is not installed, cannot display graph plot!")
        return

    agraph = AGraph(graph)
    agraph.layout(prog='dot')
    if filename is None:
        filename = tempfile.mktemp(suffix=".png")
    agraph.draw(filename)
    image = Image.open(filename)
    image.show()