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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 add_fields(self, fields):
 """ Adds all of the passed fields to the table's current field list :param fields: The fields to select from ``table``. This can be a single field, a tuple of fields, or a list of fields. Each field can be a string or ``Field`` instance :type fields: str or tuple or list of str or list of Field or :class:`Field <querybuilder.fields.Field>` """

        if isinstance(fields, string_types):
            fields = [fields]
        elif type(fields) is tuple:
            fields = list(fields)

        field_objects = [self.add_field(field) for field in fields]
        return field_objects