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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_alias(self):
 """ Gets the alias for the field or the auto_alias if one is set. If there isn't any kind of alias, None is returned. :return: The field alias, auto_alias, or None :rtype: str or None """

        alias = None
        if self.alias:
            alias = self.alias
        elif self.auto_alias:
            alias = self.auto_alias

        if self.table and self.table.prefix_fields:
            field_prefix = self.table.get_field_prefix()
            if alias:
                alias = '{0}__{1}'.format(field_prefix, alias)
            else:
                alias = '{0}__{1}'.format(field_prefix, self.name)

        return alias