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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 render(self, parts=None):
 """ Returns a two-element tuple with the ``struct`` format and values. Iterates over the applicable sub-parts and calls `render()` on them, accumulating the format string and values. Optionally takes a subset of parts to render, default behavior is to render all sub-parts belonging to the class. """

        if not parts:
            parts = self.parts

        fmt = []
        data = []

        for name, part_class in parts:
            if issubclass(part_class, Primitive):
                part = part_class(getattr(self, name, None))
            else:
                part = getattr(self, name, None)

            part_format, part_data = part.render()

            fmt.extend(part_format)
            data.extend(part_data)

        return "".join(fmt), data