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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 Mean(self):
 """Return the arithmatic mean of all values."""

    values = [v for v, _ in self.data if v is not None]
    if not values:
      return None

    # TODO(hanuszczak): Why do we return a floored division result instead of
    # the exact value?
    return sum(values) // len(values)