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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 contents(self):
 """Return the list of contained directory entries, loading them if not already loaded."""

        if not self.contents_read:
            self.contents_read = True
            base = self.path
            for entry in os.listdir(self.source_path):
                source_path = os.path.join(self.source_path, entry)
                target_path = os.path.join(base, entry)
                if os.path.isdir(source_path):
                    self.filesystem.add_real_directory(
                        source_path, self.read_only, target_path=target_path)
                else:
                    self.filesystem.add_real_file(
                        source_path, self.read_only, target_path=target_path)
        return self.byte_contents