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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 flip(self):
        '''Flip the DNA - swap the top and bottom strands.

        :returns: Flipped DNA (bottom strand is now top strand, etc.).
        :rtype: coral.DNA

        '''
        copy = self.copy()
        copy.top, copy.bottom = copy.bottom, copy.top
        copy.features = [_flip_feature(f, len(self)) for f in copy.features]
        return copy