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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 name(self):
 """ Save name which can be used for alphabetic sorting and can be turned into a kwarg. """

    base_str = 'd{}{}_'.format(self.derivative_count if
                               self.derivative_count > 1 else '', self.expr)
    for var, count in self.variable_count:
        base_str += 'd{}{}'.format(var,  count if count > 1 else '')
    return base_str