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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 get_vertex_string(self, i):
 """Return a string based on the atom number"""

        number = self.numbers[i]
        if number == 0:
            return Graph.get_vertex_string(self, i)
        else:
            # pad with zeros to make sure that string sort is identical to number sort
            return "%03i" % number