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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 crc(self):
 """ A CRC of the current vertices and entities. Returns crc: int, CRC of entity points and vertices """

        # first CRC the points in every entity
        target = caching.crc32(bytes().join(e._bytes()
                                            for e in self.entities))
        # add the CRC for the vertices
        target ^= self.vertices.crc()
        return target