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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 fixations(self):
 """ Returns all fixations that are on this image. A precondition for this to work is that a fixmat is associated with this Image object. """

        if not self._fixations:
            raise RuntimeError('This Images object does not have'
                +' an associated fixmat')
        return self._fixations[(self._fixations.category == self.category) &
                               (self._fixations.filenumber == self.image)]