class AWS::DynamoDB::BatchWrite

def str2sym key_desc
  type, value = key_desc.to_a.flatten
  case type
  when "S"  then { :s  => value }
  when "N"  then { :n  => value }
  when "SS" then { :ss => value }
  when "NS" then { :ns => value }
  else 
    raise "unhandled key type: #{type.inspect}"
  end
end