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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_columns(self, model, **fields):
 """Create new fields."""

        for name, field in fields.items():
            model._meta.add_field(name, field)
            self.ops.append(self.migrator.add_column(
                model._meta.table_name, field.column_name, field))
            if field.unique:
                self.ops.append(self.migrator.add_index(
                    model._meta.table_name, (field.column_name,), unique=True))
        return model