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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 iter_previewers(self, previewers=None):
 """Get previewers ordered by PREVIEWER_PREVIEWERS_ORDER."""

        if self.entry_point_group is not None:
            self.load_entry_point_group(self.entry_point_group)
            self.entry_point_group = None

        previewers = previewers or \
            self.app.config.get('PREVIEWER_PREFERENCE', [])

        for item in previewers:
            if item in self.previewers:
                yield self.previewers[item]