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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 overlap_size(self,tx2):
 """Return the number of overlapping base pairs between two transcripts :param tx2: Another transcript :type tx2: Transcript :return: overlap size in base pairs :rtype: int """

    total = 0
    for e1 in self.exons:
      for e2 in tx2.exons:
        total += e1.overlap_size(e2)
    return total