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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 designspace(self):
 """Get a designspace Document instance that links the masters together and holds instance data. """

        if self._designspace_is_complete:
            return self._designspace

        self._designspace_is_complete = True
        list(self.masters)  # Make sure that the UFOs are built
        self.to_designspace_axes()
        self.to_designspace_sources()
        self.to_designspace_instances()
        self.to_designspace_family_user_data()

        if self.bracket_layers:
            self._apply_bracket_layers()

        # append base style shared by all masters to designspace file name
        base_family = self.family_name or "Unnamed"
        base_style = find_base_style(self.font.masters)
        if base_style:
            base_style = "-" + base_style
        name = (base_family + base_style).replace(" ", "") + ".designspace"
        self.designspace.filename = name

        return self._designspace