code: def ecoclass_to_coderef(self, cls):
          
          code = ''
          ref = None
          for (code,ref,this_cls) in self.mappings():
              if cls == this_cls:
                  return code, ref
          return None, None
docs: Map an ECO class to a GAF code
  
          This is the reciprocal to :ref:`coderef_to_ecoclass`
  
          Arguments
          ---------
          cls : str
              GAF evidence code, e.g. ISS, IDA
          reference: str
              ECO class CURIE/ID
  
          Return
          ------
          (str, str)
              code, reference tuple