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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 _next_unused_label(self):
 """Helper method to move to the next unused label. Not intended for external use. This method will shade in any missing labels if desired, and will increment the label_count attribute once a suitable label position has been found. """

        self._next_label()

        # This label may be missing.
        if self.page_count in self._used:
            # Keep try while the label is missing.
            missing = self._used.get(self.page_count, set())
            while tuple(self._position) in missing:
                # Throw the missing information away now we have used it. This
                # allows the _shade_remaining_missing method to work.
                missing.discard(tuple(self._position))

                # Shade the missing label if desired.
                if self.shade_missing:
                    self._shade_missing_label()

                # Try our luck with the next label.
                self._next_label()
                missing = self._used.get(self.page_count, set())

        # Increment the count now we have found a suitable position.
        self.label_count += 1