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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 lines(self, code):
 """Fixes indentation for multiline strings before appending."""

        if isinstance(code, str):
            fix_indentation = self.fix_indentation
            if fix_indentation:
                code = fix_indentation(code)
            return self.append(code)
        else:
            return self.append(code)