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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(self):
        '''Plot the results of the run method.'''
        try:
            from matplotlib import pylab
        except ImportError:
            raise ImportError('Optional dependency matplotlib not installed.')

        if self.walked:
            fig = pylab.figure()
            ax1 = fig.add_subplot(111)
            ax1.plot(self.core_starts, self.scores, 'bo-')
            pylab.xlabel('Core sequence start position (base pairs).')
            pylab.ylabel('Score - Probability of being unbound.')
            pylab.show()
        else:
            raise Exception('Run calculate() first so there\'s data to plot!')