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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 MessageSetItemSizer(field_number):
 """Returns a sizer for extensions of MessageSet. The message set message looks like this: message MessageSet { repeated group Item = 1 { required int32 type_id = 2; required string message = 3; } } """

  static_size = (_TagSize(1) * 2 + _TagSize(2) + _VarintSize(field_number) +
                 _TagSize(3))
  local_VarintSize = _VarintSize

  def FieldSize(value):
    l = value.ByteSize()
    return static_size + local_VarintSize(l) + l

  return FieldSize