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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(self, indent, line):
 """Appends the given text line with prefixed spaces in accordance with the given number of indentation levels. """

        if isinstance(line, str):
            list.append(self, indent*4*' ' + line)
        else:
            for subline in line:
                list.append(self, indent*4*' ' + subline)