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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 transform_region(self, from_, to, transform_callback):
 """ Transform a part of the input string. :param from_: (int) start position. :param to: (int) end position. :param transform_callback: Callable which accepts a string and returns the transformed string. """

        assert from_ < to

        self.text = ''.join([
            self.text[:from_] +
            transform_callback(self.text[from_:to]) +
            self.text[to:]
        ])