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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 save_spectre_plot(self, filename="spectre.pdf", img_format="pdf", sigma=0.05, step=0.01):
 """ Save matplotlib plot of the spectre to a file. Args: filename: Filename to write to. img_format: Image format to use. Defaults to EPS. sigma: Full width at half maximum in eV for normal functions. step: bin interval in eV """

        d, plt = self.get_spectre_plot(sigma, step)
        plt.savefig(filename, format=img_format)