input: Write a python function to set the datatype attribute of the CustomReader class. 
  assert CustomReader().setDataType("float") is None
  assert CustomReader().datatype == 'float'
  assert CustomReader().setDataType("int") is None
  assert CustomReader().datatype == 'int'
output: class CustomReader:
      def setDataType(self, datatype):
          self.datatype = datatype