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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 change_column(self, table, column_name, field):
 """Change column."""

        operations = [self.alter_change_column(table, column_name, field)]
        if not field.null:
            operations.extend([self.add_not_null(table, column_name)])
        return operations