Get the range from the leftmost exon to the rightmost

    :return: total range
    :rtype: GenomicRange

def range(self):
    """Get the range from the leftmost exon to the rightmost

    :return: total range
    :rtype: GenomicRange
    """
    return GenomicRange(self._rngs[0].chr,self._rngs[0].start,self._rngs[-1].end)